Create a top-level Merge Request section under Settings

Context

As part of the UX Scorecard (gitlab-design#441 (closed)), a first usability test around GitLab's Merge Request page showed that the approval rules can be difficult to understand. We followed up with a usability testing study (ux-research#270 (closed)) to investigate this further and uncover new insights.

Objective

The purpose of this issue is to ideate and propose an iterative improvement to the placement of the Merge Request approvals settings. Currently, they live under Project>Settings>General>Merge Request approvals in the left sidebar.

Proposal

Move "Merge request" into own section in "Settings" called Merge request
Remove the collapse/expand buttons
Add dismissible alert in previous location (keep alert in product for 9 releases)

In a follow-up issue, we should then also update the layout for better scanability #325194, and add a link to this new section from within the Merge Request area #325240.

Problem validation

In this study, finding the Merge Request approvals setting was challenging for users who aren't familiar with the MR approvals feature. This is partially due to the fact that there are some concepts that seem related in GitLab (e.g. roles, Code Owners, protected branches) and this can send them down various paths to locate it.

Even the participants who were familiar with the approvals feature experienced hesitancy when finding the setting. This hesitancy primarily came from the fact that they weren't sure if they should look in Settings>Repository or Settings>General>Merge Requests. Some did not see the approval rules setting at first because it was lower on the page.

Quotes

P1: "Having the settings separated always confuses me a little bit because I'm not sure if I'm going to find something under General or Repository."
P2: Immediately goes to Settings>General>Merge Requests. He starts searching through the "Merge Requests" section first and then lands on "Merge commits." He continues to look and then settles on the "Merge Request approvals" section. Thinks it's not intuitive because there is Merge Requests and Merge Request approvals. So he thinks MR approvals should be under the Merge Request section.
P3: "The natural place is Settings>Repository..." He first searches in Repository settings then clarifies the task, then looks at the Merge Request section, then the Merge Request approvals section. Expected it to be found in Settings but didn't expect to see it under "General." He'd expect to see MR-related stuff as a submenu.
P4: He hasn't set up this part but what he would assume is that he should go to Settings>Members. He assumes the maintainer role should grant permission to be a reviewer in here. He then considers going to Project>Merge Requests and changing the MR Assignee. When I emphasized "all" he then thought he should bulk update the assignee for all open MRs. After receiving another hint, he then thinks to go to Settings>General> Repository but he doesn't find it there. His last resort is to go to Settings>General and finally sees Merge Request approvals.
P5: He first checks the Merge Request page to see where he can configure MR approvals. He then moves on to Project>Settings but he spends a lot of time scrolling around and looking for the right place. He notes that he missed the Merge Request approvals setting area because he hadn't scrolled down the page.

Solution validation

The proposal was validated in the research around navigating to settings (Insight).