CI: Optimize docker build

[mion00]

This PR is built on top of #1655, augmenting it with the new project setup (pyproject.toml instead of requirements.txt) and CI pipeline.

Description

• Always build the Docker image and Python package (pushing only with tag or dev branch) as part of the Github pipeline.
  This way we can easily catch any problem in the build process, without having to first merge the changes inside dev.
• Use Python package built during the build_package job for building the Docker image. This way we avoid having to copy the entire project source inside the image, reducing the image size.
  At the same time this process "mimics" the step an end-user of the package does (a pip install), so we can verify that the package can indeed install correctly.
• Optimize the docker build cache by using RUN --mount=type=cache to speed up the process between subsequent builds.
• Small fix to the pyproject.toml: exclude the static assets inside docs. folder, otherwise they get included as part of the Python package, unnecessarily bloating it

[acockburn]

The build failed with the new docker file:

https://github.com/AppDaemon/appdaemon/actions/runs/4303953648/jobs/7504338740

[mion00]

Yeah the changes from #1655 where not exactly up-to-date with the state of the projects, for instance the use of requirements.txt breaks the build.
I am working on a fix in this PR.