Improve error message for webhook name description

The length constraints were added to the `web_hooks` table when the
columns were migrated
https://gitlab.com/gitlab-org/gitlab/-/merge_requests/141977.

This change adds corresponding model validations to improve the error
messages returned.

Changelog: changed

app/models/concerns/web_hooks/hook.rb

@@ -65,6 +65,8 @@ module Hook
       validates :interpolated_url, public_url: true, if: ->(hook) { hook.url_variables? && hook.errors.empty? }
       validates :custom_headers, json_schema: { filename: 'web_hooks_custom_headers' }
       validates :custom_webhook_template, length: { maximum: 4096 }
+      validates :name, length: { maximum: 255 }
+      validates :description, length: { maximum: 2048 }
 
       enum :branch_filter_strategy, {
         wildcard: 0,

spec/support/shared_examples/models/concerns/web_hooks/web_hook_shared_examples.rb

@@ -18,6 +18,8 @@
   describe 'validations' do
     it { is_expected.to validate_presence_of(:url) }
     it { is_expected.to validate_length_of(:custom_webhook_template).is_at_most(4096) }
+    it { is_expected.to validate_length_of(:name).is_at_most(255) }
+    it { is_expected.to validate_length_of(:description).is_at_most(2048) }
 
     describe 'url_variables' do
       it { is_expected.to allow_value({}).for(:url_variables) }