[RUN AS-IF-FOSS] Move "Allow users to request access" setting to a new subsection "Membership"

What does this MR do?

This is a fix to the reverted MR !68544 (merged), it:

• It adds a new subsection "Membership" to group's settings under "Permissions, LFS, 2FA"
• It moves "Allow users to request access" item to be under the newly created subsection "Membership"

Screenshots

How to setup and validate locally (strongly suggested)

1. Navigate to a group's settings (using a user that's a group owner)
2. Observe the changes in the "Permissions, LFS, 2FA" section

Does this MR meet the acceptance criteria?

Conformity

• I have included changelog trailers, or none are needed. (Does this MR need a changelog?)
  • I haven't added a changed log, the change is under a feature flag
• I have properly separated EE content from FOSS, or this MR is FOSS only. (Where should EE code go?)
• I have self-reviewed this MR per code review guidelines.
• I have followed the style guides.
• This change is backwards compatible across updates, or this does not apply.

Related to #330029 (closed)