[FF] custom_code_dropdown_clients -- custom "Open with" clients in the Code dropdown

Summary

Roll out the feature currently behind the custom_code_dropdown_clients feature flag.

• DRI: @ms.mondrian
• Team Slack channel: #g_create_source-code

Merged in 19.5:

• !233416 (merged) — the code_dropdown_custom_clients setting and its validation
• !244658 (merged) — the admin form
• !244659 (merged) — rendering the entries in the Code dropdown
• !244660 (merged) — documentation

What could go wrong?

The blast radius is small. The setting starts empty, and with an empty list the Code dropdown is exactly as it is today. Entries only appear after an administrator adds them, and the rendering path re-checks each URL scheme before building a link.

Worth noting: this is an instance-wide admin setting, so on GitLab.com nothing changes for users unless GitLab itself configures entries. The real goal here is validating the code, then setting default_enabled: true so GitLab Self-Managed and GitLab Dedicated get the feature.

Rollout

Non-production

/chatops gitlab run feature set custom_code_dropdown_clients true --dev --pre --staging --staging-ref

Production

/chatops gitlab run feature set custom_code_dropdown_clients true

Before global rollout

• Docs and version history updated — !244660 (merged) covers the page; when the flag defaults to on, add GitLab Dedicated to the Offering line, since Dedicated can't use flags that are off by default
• rollout_issue_url filled in in config/feature_flags/beta/custom_code_dropdown_clients.yml (small MR, I can open it once this issue exists)

Cleanup

Once stable: set default_enabled: true, then remove the flag and its YAML file.

/chatops gitlab run feature delete custom_code_dropdown_clients --dev --pre --staging --staging-ref --production

Rollback

/chatops gitlab run feature set custom_code_dropdown_clients false