* implement manifest caching; refactor config with includes, and generate from ENVs in entrypoint.sh
- disabled by default; enable with -e ENABLE_MANIFEST_CACHE=true
- default times and regexes are a wild guess, make sure to tune for your use case.
- add manifest caching/anti-ratelimit usage note to README
- add -e ENABLE_MANIFEST_CACHE=true to examples, some wording changes
- add -e ENABLE_MANIFEST_CACHE=true to one the steps in test workflow.
