ci: add gha caching for dev images

[pratikbin]

• I think we should skip caching for production image building
• and comment below if you want to build this for more multiple platforms, I can try some things

[derneuere]

Thanks for the pull request. Didn't knew that this feature exists 😄 I agree production image should be build from scratch 👍
I can't really test different architectures and we have alot of difficult dependencies in the backend that only crash on startup and not on build.

We have this base image "librephotos-dependencies" for the backend. This image is large (8GB), because we install all of the build dependencies. If you want to work more on this, than that would be awesome #15

https://github.com/LibrePhotos/librephotos-docker/blob/main/backend/dependencies/Dockerfile

I think that the dependency image would also need this change, but you can address this in a separate commit 👍