Current package registry for RubyGems does not work with Bundler, because it implements neither the [compact index](https://guides.rubygems.org/rubygems-org-compact-index-api/) or the [dependency API](https://guides.rubygems.org/rubygems-org-api/). As a result, bundler complains about finding non-existing dependencies when installing anything with dependency: `revealed dependencies not in the API or the lockfile`.
This patch provides a minimal implementation for the compact index API to solve this issue. Specifically, we implemented a version that does not cache the results / do incremental updates; which is consistent with the current implementation.
Testing:
* Modified existing integration tests.
* Manually Verified bundler is able to parse the served versions / info file.
Reviewed-on: https://codeberg.org/forgejo/forgejo/pulls/3811
Reviewed-by: Earl Warren <earl-warren@noreply.codeberg.org>
Co-authored-by: Haoyuan (Bill) Xing <me@hoppinglife.com>
Co-committed-by: Haoyuan (Bill) Xing <me@hoppinglife.com>
