Additional Args and configurable docker image source

[timoxd7]

Configurable Docker image source

Added esp_idf_root to be used as source for the docker image. Can be used to select docker images hosted on different accounts or servers.

Additional arguments

Added additional_args to add custom arguments to the docker run command. Can be used to enable ccache usage, only add ccache ci action and add the following lines:

-v ./.ccache:/root/.ccache -e CCACHE_DIR=/root/.ccache

Only make sure the .ccache folder is created if no cache was already build (always on the first run).