Pull mirror API: extend response with mirror related fields

Contributes to https://gitlab.com/gitlab-org/gitlab/-/issues/494294

**Problem**

Existing endpoint does not return information about mirror configuration
state. It's not possible to see mirror settings using Pull mirror API.

**Solution*

Expose missing settings.

Changelog: added

doc/api/project_pull_mirroring.md

 ---
-stage: Data Stores
-group: Tenant Scale
+stage: Create
+group: Source Code
 info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://handbook.gitlab.com/handbook/product/ux/technical-writing/#assignments
 ---
 
@@ -15,6 +15,7 @@ You can manage project [pull mirroring](../user/project/repository/mirror/pull.m
 ## Get a project's pull mirror details
 
 > - [Introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/354506) in GitLab 15.6.
+> - [Extended response](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/168377) to include mirror configuration information in GitLab 17.5. The following configuration settings are included: `enabled`, `mirror_trigger_builds`, `only_mirror_protected_branches`, `mirror_overwrites_diverged_branches`, and `mirror_branch_regex`.
 
 Return the details of a project's [pull mirror](../user/project/repository/mirror/index.md).
 
@@ -34,6 +35,24 @@ Example request:
 curl --request GET --header "PRIVATE-TOKEN: <your_access_token>" "https://gitlab.example.com/api/v4/projects/:id/mirror/pull"
 ```
 
+If successful, returns [`200 OK`](rest/troubleshooting.md#status-codes) and the
+following response attributes:
+
+| Attribute                             | Type            | Description                                                                 |
+|---------------------------------------|-----------------|-----------------------------------------------------------------------------|
+| `id`                                  | integer         | The unique identifier of the mirror configuration.                          |
+| `last_error`                          | string or null  | The most recent error message, if any. `null` if no errors occurred.        |
+| `last_successful_update_at`           | string          | Timestamp of the last successful mirror update.                             |
+| `last_update_at`                      | string          | Timestamp of the most recent mirror update attempt.                         |
+| `last_update_started_at`              | string          | Timestamp when the last mirror update process started.                      |
+| `update_status`                       | string          | The status of the mirror update process.                                    |
+| `url`                                 | string          | URL of the mirrored repository.                                             |
+| `enabled`                             | boolean         | Indicates whether the mirror is active or inactive.                         |
+| `mirror_trigger_builds`               | boolean         | Determines if builds should be triggered for mirror updates.                |
+| `only_mirror_protected_branches`      | boolean or null | Specifies if only protected branches should be mirrored. `null` if not set. |
+| `mirror_overwrites_diverged_branches` | boolean         | Indicates if diverged branches should be overwritten during mirroring.      |
+| `mirror_branch_regex`                 | string or null  | Regex pattern for filtering which branches to mirror. `null` if not set.    |
+
 Example response:
 
 ```json
@@ -44,7 +63,12 @@ Example response:
   "last_update_at": "2020-01-06T17:32:02.823Z",
   "last_update_started_at": "2020-01-06T17:31:55.864Z",
   "update_status": "finished",
-  "url": "https://*****:*****@gitlab.com/gitlab-org/security/gitlab.git"
+  "url": "https://*****:*****@gitlab.com/gitlab-org/security/gitlab.git",
+  "enabled": true,
+  "mirror_trigger_builds": true,
+  "only_mirror_protected_branches": null,
+  "mirror_overwrites_diverged_branches": false,
+  "mirror_branch_regex": null
 }
 ```
 

lib/api/entities/pull_mirror.rb

@@ -14,6 +14,19 @@ class PullMirror < Grape::Entity
       expose :last_update_at, documentation: { type: 'dateTime', example: '2020-01-06T17:32:02.823Z' }
       expose :last_update_started_at, documentation: { type: 'dateTime', example: '2020-01-06T17:32:02.823Z' }
       expose :last_successful_update_at, documentation: { type: 'dateTime', example: '2020-01-06T17:32:02.823Z' }
+      expose :enabled, documentation: { type: 'boolean', example: false }
+      expose :mirror_trigger_builds, documentation: { type: 'boolean', example: false }
+      expose :only_mirror_protected_branches, documentation: { type: 'boolean', example: false }
+      expose :mirror_overwrites_diverged_branches, documentation: { type: 'boolean', example: false }
+      expose :mirror_branch_regex, documentation: { type: 'string', example: 'branch_name' }
+
+      delegate :project, to: :object
+      delegate :mirror_trigger_builds, :only_mirror_protected_branches, :mirror_overwrites_diverged_branches,
+        :mirror_branch_regex, to: :project
+
+      def enabled
+        object.project.mirror
+      end
     end
   end
 end

spec/fixtures/api/schemas/project_mirror.json

@@ -7,7 +7,12 @@
     "last_update_at",
     "last_update_started_at",
     "last_successful_update_at",
-    "last_error"
+    "last_error",
+    "enabled",
+    "mirror_trigger_builds",
+    "only_mirror_protected_branches",
+    "mirror_overwrites_diverged_branches",
+    "mirror_branch_regex"
   ],
   "properties": {
     "id": {
@@ -42,7 +47,31 @@
         "string",
         "null"
       ]
+    },
+    "enabled": {
+      "type": "boolean"
+    },
+    "mirror_trigger_builds": {
+      "type": "boolean"
+    },
+    "only_mirror_protected_branches": {
+      "type": [
+        "boolean",
+        "null"
+      ]
+    },
+    "mirror_overwrites_diverged_branches": {
+      "type": [
+        "boolean",
+        "null"
+      ]
+    },
+    "mirror_branch_regex": {
+      "type": [
+        "string",
+        "null"
+      ]
     }
   },
   "additionalProperties": false
-}
\ No newline at end of file
+}