Add committer approval API attribute

Merge Requests Approvals can be restricted to prevent the merge
request author or merge request committers from self approving. The
author restriction is already available in the API, but the committer
restriction was not.

ee/changelogs/unreleased/jramsay-committer-approval-api.yml

+---
+title: Add missing merge request committer approval setting to API
+merge_request: 15019
+author: jramsay
+type: changed

ee/lib/api/project_approvals.rb

@@ -28,8 +28,9 @@ module API
           optional :approvals_before_merge, type: Integer, desc: 'The amount of approvals required before an MR can be merged'
           optional :reset_approvals_on_push, type: Boolean, desc: 'Should the approval count be reset on a new push'
           optional :disable_overriding_approvers_per_merge_request, type: Boolean, desc: 'Should MRs be able to override approvers and approval count'
-          optional :merge_requests_author_approval, type: Boolean, desc: 'Should authors be able to self approve merge requests'
-          at_least_one_of :approvals_before_merge, :reset_approvals_on_push, :disable_overriding_approvers_per_merge_request, :merge_requests_author_approval
+          optional :merge_requests_author_approval, type: Boolean, desc: 'Should merge request authors be able to self approve merge requests; `true` means authors cannot self approve'
+          optional :merge_requests_disable_committers_approval, type: Boolean, desc: 'Should committers be able to self approve merge requests'
+          at_least_one_of :approvals_before_merge, :reset_approvals_on_push, :disable_overriding_approvers_per_merge_request, :merge_requests_author_approval, :merge_requests_disable_committers_approval
         end
         post '/' do
           project_params = declared(params, include_missing: false, include_parent_namespaces: false)

ee/lib/ee/api/entities.rb

@@ -367,6 +367,7 @@ module EE
         expose :reset_approvals_on_push
         expose :disable_overriding_approvers_per_merge_request
         expose :merge_requests_author_approval
+        expose :merge_requests_disable_committers_approval
       end
 
       class Approvals < Grape::Entity

ee/spec/fixtures/api/schemas/public_api/v4/project_approvers.json

@@ -5,6 +5,7 @@
     "disable_overriding_approvers_per_merge_request": { "type": ["boolean", "null"] },
     "reset_approvals_on_push": { "type": "boolean" },
     "merge_requests_author_approval": { "type": ["boolean", "null"] },
+    "merge_requests_disable_committers_approval": { "type": ["boolean", "null"] },
     "approvers": {
       "type": "array",
       "items": {

ee/spec/requests/api/project_approvals_spec.rb

@@ -66,13 +66,15 @@ describe API::ProjectApprovals do
           project.reset_approvals_on_push = false
           project.disable_overriding_approvers_per_merge_request = true
           project.merge_requests_author_approval = false
+          project.merge_requests_disable_committers_approval = true
           project.save
 
           settings = {
             approvals_before_merge: 4,
             reset_approvals_on_push: true,
             disable_overriding_approvers_per_merge_request: false,
-            merge_requests_author_approval: true
+            merge_requests_author_approval: true,
+            merge_requests_disable_committers_approval: false
           }
 
           post api(url, current_user), params: settings