Replaces the previously used Docker Hub autobuild infrastructure.
This allows for more flexible configuration of the build process,
at the expense of some extra maintenance of CI workflow files
required.
These two arguments can be used to reduce the size of the Docker
image:
- Setting IDF_CLONE_SHALLOW enables shallow cloning.
- Setting IDF_INSTALL_TARGETS to the comma separated list of targets
results in toolchains being installed only for these targets.
