feat: create docker images for standalone use

[chetan]

Hi,

I noticed there's no official docker build for the project. The below is a simple build which serves using nginx:alpine. If you'd like to set up an official repository, let me know and I can update the repository name in the readme below.

chetan

[rchl]

If you'd like to set up an official repository, let me know and I can update the repository name in the readme below.

I'm OK with having an official docker image for this project but then I'd expect the docker images to be made automatically from CI. Similar to how it's done from the tileboard-addon repo - https://github.com/resoai/TileBoard-addon/blob/b6a67d80c82edb634503110b31de91ed6e1bbb79/.github/workflows/on_tag.yaml#L22-L22

[chetan]

@rchl added the workflow step for building and pushing the docker image. Have not tested all the way through, but it should work.

[rchl]

Thanks.