Support installing plugins from GitLab repositories

What feature would you like to see?

Would the project be open to supporting plugin installation directly from GitLab repository URLs through /plugins install <url>, alongside the existing GitHub installation flow?

For organizational, security, or distribution reasons, some plugins can only be hosted on internal GitLab instances. Requiring users to download and extract those plugins manually makes the installation documentation provider-specific and less convenient. Supporting GitLab through the existing /plugins command would keep the workflow and documentation consistent across hosting providers.

Useful source forms would include GitLab.com and self-managed GitLab repository URLs, with bare repository URLs and explicit branch, tag, or commit URLs handled similarly to the GitHub flow.

Additional information

An implementation is available in #1801 for discussion and reference. It supports both plugin engines and includes tests and English/Chinese documentation. It does not add token or credential storage; the GitLab instance and repository must already be reachable from the CLI.

This issue is intended to confirm whether GitLab plugin installation is planned or whether maintainers are open to this direction, and to gather any preferred scope or design constraints before proceeding further.

Start by reviewing the existing GitHub flow for /plugins install <url> and implementation #1801, which includes support for both plugin engines, tests, and English/Chinese documentation. The proposed work would need to establish the preferred scope for GitLab.com and self-managed URLs, including branch, tag, and commit forms, before implementation can be considered done.