This extracts some of the code from #511 but without breaking changes
* Use `PathBuf` instead of `String` where dealing with files
* Parse keep_alive as u64
* More config tests to crash if martin output contains warnings or
errors
* Change docker image to use `entrypoint` -- so that Martin can be used
as a command:
```bash
docker run maplibre/martin <parameters>
```
* The docker image is now tested the same way as in the CI tests
* Added a few changes to the justfile
Fixes#436
* Add justfile to simplify running all the tests
* Save all PBF outputs to the text files
* Consolidate all tests to reuse the same code
* Consolidate database initialization
* updated readme with the new instructions
Note that while this PR creates "expected" files, the CI cannot validate
the generated results because the output is not stable. Eventually we
may try to output just the non-geometry values to have reasonable tests
comparing against the expected results.
