Add a description to approval settings

What does this MR do?

Creates a consistent description for merge request approval settings in all levels of GitLab and removes the individual links.

Screenshots or Screencasts (strongly suggested)

	Before	After
Admin Area
Group
Project

How to setup and validate locally (strongly suggested)

1. Open each area Admin Area > Push Rules Group > Settings > General Project > Settings > General
2. Check the help link

Does this MR meet the acceptance criteria?

Conformity

• I have included changelog trailers, or none are needed. (Does this MR need a changelog?)
• I have added/updated documentation, or it's not needed. (Is documentation required?)
• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
• I have followed the style guides.
• This change is backwards compatible across updates, or this does not apply.

Availability and Testing

• I have added/updated tests following the Testing Guide, or it's not needed. (Consider all test levels. See the Test Planning Process.)
• I have tested this MR in all supported browsers, or it's not needed.
• I have informed the Infrastructure department of a default or new setting change per definition of done, or it's not needed.