Description

• Move the proto-gen dependencies to a new file. They are only used for proto file generation when we update the opentelemetry-proto version. People run into build issues when installing grpcio-tools and that shouldn't block them from running lint/docs etc on changes that are unrelated.
• More conservative approach to version pinning to avoid surprises.
• Expand the black ignore list, otherwise black would format everything in the virtual environment.
• Update the testenv in the lint stage to work on any Python version.

I verified that lint, docs, and other steps work on py3.8 to py3.11 so contributors with any of the versions should be able to run them locally without any issues.