Add environment variable OTEL_EXPORTER_OTLP_CHANNEL_OPTIONS for grpc channel options

[vishaalram02]

Description

Fixes #4278. Also adds support for many other grpc core configurations.

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

Happy to add unit tests, but wanted to get an initial review first on the changes.

• Test A

Does This PR Require a Contrib Repo Change?

• Yes. - Link to PR:
• No.

Checklist:

• Followed the style guidelines of this project
• Changelogs have been updated
• Unit tests have been added
• Documentation has been updated

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: vishaalram02 / name: Vishaal Ram (6c3efd7, 42c92fb, 4a7a13d)

[vishaalram02]

@xrmx Was wondering if you have the chance to take a quick look at this?

[xrmx]

These env vars come from https://opentelemetry.io/docs/specs/otel/protocol/exporter/ , if yours is custom to the python agent we can't use the same prefix. Do other languages have something like this?

[vishaalram02]

Ah this is specific to https://github.com/grpc/grpc which I don't believe every languages uses. If it doesn't make sense to introduce these options in otel python, this may be more of an issue with the underlying library.