Add managing protected branches as custom permission

...ascripts/projects/settings/components/access_dropdown.vue

...javascripts/protected_branches/protected_branch_create.js

app/controllers/groups/settings/repository_controller.rb

app/controllers/projects/settings/ci_cd_controller.rb

app/controllers/projects/settings/repository_controller.rb

app/policies/projects/branch_rule_policy.rb

app/validators/json_schemas/member_role_permissions.json

doc/api/graphql/reference/index.md

doc/user/custom_roles/abilities.md

.../controllers/ee/projects/protected_branches_controller.rb

...controllers/ee/projects/settings/repository_controller.rb

ee/app/policies/ee/project_policy.rb

ee/config/custom_abilities/admin_protected_branch.yml

ee/lib/ee/sidebars/projects/menus/settings_menu.rb

...rollers/ee/projects/protected_branches_controller_spec.rb

...ntrollers/projects/settings/repository_controller_spec.rb

ee/spec/features/projects/protected_branches_spec.rb

.../features/projects/settings/ee/protected_branches_spec.rb

...pec/frontend/protected_environments/add_approvers_spec.js

...otected_environments/create_protected_environment_spec.js