fix(docker): use tini as entrypoint

[fatih-acar]

This should workaround #5400 where child git processes are not reaped correctly.

We could have used init: true in docker compose, but this would not work for k8s deployments...

[codspeed-hq]

CodSpeed Performance Report

Merging #5459 will improve performances by 27.54%

_{Comparing fac-workaround-process-reap (eea8257) with stable (dd1cc18)}

Summary

⚡ 1 improvements
✅ 9 untouched benchmarks

Benchmarks breakdown

	Benchmark	stable	fac-workaround-process-reap	Change
⚡	test_schemabranch_duplicate	418.9 µs	328.5 µs	+27.54%