Use GitHub App per repository for cases where the App needs content write access to a repository

[trask]

Based on @CodeBlanch's https://github.com/open-telemetry/community/issues/2127#issuecomment-2704773410

As we move towards using GitHub App for automation needs (https://github.com/open-telemetry/community/blob/main/assets.md#otelbot), sometimes the GitHub App needs content write access to a repository.

Instead of elevating the default otelbot GitHub App permissions, we should create a new App per repository that only has permissions scoped to that repository.

Trying this out first with opentelemetry-java-contrib: https://github.com/open-telemetry/opentelemetry-java-contrib/blob/11c3dda26b9ed5c91803f8e12e5411a272695cec/.github/workflows/auto-spotless-apply.yml#L40