Rephrase Merge Request Maintainer Edit

EE port https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/5831

What does this MR do?

Merge Request's 'allow edits from maintainer' functionality has to be rephrased.

The UI text is changed to "Allow commits from members who can merge to the target branch."

Are there points in the code the reviewer needs to double check?

Please see if the following rephrasing is good

DB Column
allow_maintainer_to_push	allow_collaboration
MergeRequest model:
maintainer_push_possible	collaboration_push_possible
can_allow_maintainer_to_push(user)	can_allow_collaboration_push(user)
Project model
branch_allows_maintainer_push?(user, branch_name)	branch_allows_collaboration_push?
Helper
allow_maintainer_push_unavailable_reason	allow_collaboration_unavailable_reason
Vue
mr_widget_maintainer_edit.vue	mr_widget_allow_collaboration.vue
MRWidgetMaintainerEdit	MRWidgetAllowCollaboration
WidgetMaintainerEdit	WidgetAllowCollaboration
mr-widget-maintainer-edit	Mr-widget-allow-collaboration
maintainerEditAllowed	allowCollaboration

Why was this MR needed?

The phrase maintainer will be reserved, in order to replace master. See #42751 (closed)

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Conform by the code review guidelines
  • Has been reviewed by a UX Designer
  • Has been reviewed by a Frontend maintainer
  • Has been reviewed by a Backend maintainer
  • Has been reviewed by a Database specialist
• Conform by the merge request performance guides
• Conform by the style guides
• If you have multiple commits, please combine them into a few logically organized commits by squashing them
• Internationalization required/considered
• End-to-end tests pass (package-and-qa manual pipeline job)

What are the relevant issue numbers?

Related to #42751 (closed)