Docker configuration updates

[KeithB]

2 general themes for this PR:

• Improve standalone container setup and add compose.
• Consolidate standalone and HA build and run as much as possible to reduce add-on/container maintenance from future predbat changes.

Assumptions:

• Majority of future work will be predbat.py and/or hass.py. On this basis, these changes reduce overhead for future changes.
• Supervisor token is always and only visible to top level run.sh when running as add-on.

Following changes made in this PR:

• Standalone container moved to Python3 Debian Slim - saves > 300MB container size. Also updated to build from the same requirements.txt as addon. Minor tweak to requirements.txt.
• startup.py tweaked (and renamed) to a general bootstrap - start is outside this now. Download based on predbat.py rather than apps.yaml. Will also only download apps.yaml if not found to avoid overwriting existing configs.
• Single run.sh for container and add-on config. Different behaviour for restarts - auto restart if add-on but falls back to container properties (e.g. compose) when running as standalone container. (ASSUMPTION: supervisor token is always and only visible when running as add-on)
• Added docker compose to allow simple setup of standalone docker container.
• Documentation update

Other:

• WARNING: Standalone container setup has been running stably for several days. Add-on install no HAOS not tested (no environment available) but code lines up. Recommend testing before accepting PR to release.

[springfall2008]

Sorry I haven't merged this, I don't understand the implications of the change but it appears like it might overwrite the local version of predbat when started which I'm not so sure about.