Non-standard Buf workspaces support

[buildbreaker]

Using the plugin with the connect-kotlin repository yields the following error when executing ./gradlew bufGenerate at the root directory:

* What went wrong:
Execution failed for task ':crosstests:google-javalite:bufGenerate'.
> > arguments: [/Users/buildbreaker/.gradle/caches/modules-2/files-2.1/build.buf/buf/1.17.0/5f7879fa647d2fa6a9cfeaf1f56ad60f7080b0fa/buf-1.17.0-osx-aarch_64.exe, generate, --output, /Users/buildbreaker/development/connect-kotlin1/crosstests/google-javalite/build/bufbuild/generated]
  > exit code: 1
  >    stdout: (empty)
  >    stderr: (below)
  > Failure: buf.gen.yaml: does not exist