Configurable max backoff for GRPC exporter

[awoimbee]

Description

Fixes #4331

This makes it so _create_exp_backoff_generator is called with self._MAX_RETRY_TIMEOUT instead of a local var, like absolutely everywhere else, in the grpc exporter.

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue) (kinda as it fixes How to make Sentry with OTel integration work in gunicorn + gevent ? getsentry/sentry-python#3781)
• 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

• tox

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

[awoimbee]

Bump. I don't think there is any potential downside to merging this