Hermetic Build does not support `.OwlBot-hermetic.yaml` for _new_ standalone libraries

[diegomarquezp]

standalone == non-monorepo

Inside an empty folder with a single generation_config.yaml, the generated library fails to be fully "unpacked" (part of postprocessing) due to the default .OwlBot-hermetic.yaml assuming a monorepo structure:

sdk-platform-java/hermetic_build/library_generation/templates/owlbot.yaml.monorepo.j2

Line 17 in 49a7ae5

- "/{{ module_name }}/grpc-google-.*/src"

Where module_name is the monorepo folder (e.g. java-alloydb).

This results in the wrong folder structure:

hi on] diegomarquezp:test-new-library$ ls
total 44K
drwxr-x---  5 diegomarquezp primarygroup 4.0K May 27 20:54 .
drwxr-x--- 75 diegomarquezp primarygroup 4.0K May 23 19:17 ..
-rw-r-----  1 diegomarquezp primarygroup  402 May 23 19:37 generation_config.yaml
drwxr-xr-x  2 diegomarquezp primarygroup 4.0K May 27 19:30 .github
drwx------  7 diegomarquezp primarygroup 4.0K May 27 19:30 output
-rw-r--r--  1 diegomarquezp primarygroup 1.1K May 27 19:30 owlbot.py
-rw-r--r--  1 diegomarquezp primarygroup 8.8K May 27 19:30 README.md
-rw-r--r--  1 diegomarquezp primarygroup  699 May 27 19:30 .repo-metadata.json
drwxr-xr-x  6 diegomarquezp primarygroup 4.0K May 27 19:30 v1alpha
-rw-r--r--  1 diegomarquezp primarygroup    0 May 27 19:30 versions.txt

Notice the v1alpha folder. This folder is meant to be "unpacked" by the postprocessing workflow.

The expected output is similar to what we see in HW repos.

cc: @zhumin8

[blakeli0]

This does not affect any full-service client libraries. It only affect someone who tries to generate a standalone library using hermetic build.
Hence this is only a problem if we try to migrate self-service customers to hermetic build or 1PP.