RFC: Alternative git forge to GitHub

GitHub is not open source. GitHub Actions run on proprietary runners and we're increasingly relying on CI/CD pipelines based on them.

We need to establish a reliable alternative solution which we can start adopting as a mirror/backup for the time being and, in case of service disruptions, policy or billing changes, easily migrate to it.

The features we're interested in are:

- Plain git hosting
- Releases/Binaries
- CI/CD (GitHub Actions)
- Static serving capabilities (GitHub Pages)
- Issue trackers

Those features may be provided by different solutions, provided they can be integrated easily. Bonus points if the suggested products are open source and self-hostable themselves.