Enable Multiarchitecture build for Docker Container

[whatever4711]

Hi together,

let me suggest a new structure for your build:
It would be great if Docker builds are separated from the source repository.

For Docker I already setup a multiarchitecture repository whatever4711/docker-gitea, which builds Containers for amd64, i386, arm64, and arm32 with the same basic Dockerfile on CircleCI. Additionally, it tags those images accordingly, such that the call docker run -it -p 2222:22 -p 3000:3000 whatever4711/gitea downloads the version for your system and there is no need for several Dockerhub repositories anymore.

Referencing issue #2607 and PR #2927

Best regards

[sapk]

In previous PR related to docker (at least #1985), I try to setup to allow that and making a sub makefile under docker folder. That way we could keep it inside gitea repo. The direction that was taken was to keep gitea directly related stuff, like documentation, inside the same repo.
As for multi-arch, now that docker cli will support it natively we should wait for it to become stable. I previously make using the earliest github.com/estesp/manifest-tool (#1615) but split into multiple step to ease the process of reviewing as not all maintainers use docker. We could definitly improve my first try with your code for multi-arch image.

[sapk]

I think we can close this as we provide multi-arch image now. We only build them for linux/amd64 and arm64 but the base is done. There is other issues to track missing platform like arm32 for rpi.
Feel free to re-open if needed.