Draft: Add UI to trust/untrust a user

What does this MR do and why?

UI-side follow-up to !123430 (merged) and part of https://gitlab.com/gitlab-org/gl-security/security-engineering/security-automation/spam/spamcheck/-/issues/17

Adds UI elements to allow admins to trust/untrust users for purposes of creating issues, notes, snippets, etc. that are detected to be possible spam.

We use UserCustomAttributes to indicate when a user is trusted to create possible spam. These UI changes expose that capability to admin users in the user admin panel and the abuse report dashboard.

Screenshots or screen recordings

Before	After

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. Log into your GDK as an admin
2. Visit /admin/users and ensure there's a Trusted tab
3. Visit /admin/spam_logs
4. Ensure there's a Trust user button on each row
5. Click the Trust user button on one spam log and note the user
6. Revisit /admin/users?filter=trusted
7. Ensure the newly trusted user is there and that there's an Untrust user action available in the dropdown menu.
8. Click the Untrust user button and confirm the action
9. Ensure that the user no longer shows up in the Trusted tab
10. Visit /admin/abuse_reports
11. Select the first report
12. Click the Actions button
13. Select Trust user
14. Verify that the user now appears in the Trusted tab in /admin/users
15. Repeat steps 10-14 but also check the Close report checkbox and verify the Abuse report is closed in /admin/abuse_reports

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

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