Update related issues/merge requests widgets
<!--IssueSummary start--> <details> <summary> Everyone can contribute. [Help move this issue forward](https://handbook.gitlab.com/handbook/marketing/developer-relations/contributor-success/community-contributors-workflows/#contributor-links) while earning points, leveling up and collecting rewards. </summary> - [Close this issue](https://contributors.gitlab.com/manage-issue?action=close&projectId=278964&issueIid=426315) </details> <!--IssueSummary end--> ### Issue - The `Create merge request/branch` button is super useful, but its current placement seems odd and it's overly prominent on the page - It's currently sort of floating to the right - On edit, it's [easily confused](https://gitlab.com/gitlab-org/gitlab/-/issues/378018#note_1158588720) with the `Save changes` button - The other widgets (related issues, tasks, etc) are collapsible and have a action buttons; the MR and branch ones do not - We have two separate widgets for related MRs and branches; could we combine them? ### Proposal | Current | Proposal | | ------ | ------ | |![Group_5](/uploads/1f6a1b4d2ab44be311a1d90b8bed5305/Group_5.png) |![Group_4](/uploads/c7233f0d33d1ac279e5957bee47a080e/Group_4.png) | | Current | Proposal | | ------ | ------ | |![Screenshot_2023-09-26_at_1.08_1](/uploads/d96e8857207a7311859ff75e5db7b24e/Screenshot_2023-09-26_at_1.08_1.png) |![Group_2](/uploads/c48d0abc1a00738f6bb927d9223a636b/Group_2.png) |
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