Add redirect UI to Protected branches section

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Context

Per &17598 the Protected branches section was removed, to reduce redundancy and reduce confusion about redundant sections #388149 (comment 2125778390).

Design retrospective

A banner was introduced in #523300 (closed). However, customers were confused about this change, and several GitLab team members were unaware of the change.

@andr3 Slack

It's always sensitive to navigate customer expectations about these type of very necessary changes for progress.

If customers and internal team members were unaware of the section removal, despite the banner, the design of the removal could have been improved as well.

Few reasons I suspect this banner didn't work:

• GitLab is information dense and text-heavy as it is. Sometimes, it's difficult for users to parse out what information is actually important.
• There are too many banners and alerts in GitLab. If everything is important, nothing is.
• Perhaps a dynamic, interactive redirect to the Branch rules section would have been a good intermediary step to completely removing the section, rather than just having a static banner. Whether or not this is over designed for a section removal is a different question.
• People don't read.
• Slack @mvanremmerden Additionally, based on data we had collected in the past, we also know that our self-managed users often are many milestones behind (average of 8 minor versions if I remember correctly), and then often jump from one major version to another. If they then jump from eg. 17.9 to 18.6, but the banner was only visible for them from 18.1 to 18.4, they will actually never have seen it at all.

Design proposal

Add an intermediary interactive redirect to Branch rules, to give users awareness of the section moving and give users a path forward.

🎨 Figma

Proposal (minimum)	Proposal (illustrative)
Pros/cons +easier to implement -not as illustrative	Note: This doesn't have to be an overlay of the user's actual Protected branches section. It could be a generic section, or even a static image (may not scale well responsively) Pros/cons +gives visual hint at the content that was previously there -more complicated to implement in a responsive way