[DRAFT] generalize OTLP-HTTP exporter

[herin049]

Description

Fixes #3439 and #4171

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

• 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

[DylanRussell]

If the only reason for keeping requests.Session around is to keep backward compatability with _OTEL_PYTHON_EXPORTER_OTLP_HTTP_CREDENTIAL_PROVIDER than I think we shouldn't bother..

The Google auth library does have a urllib3 equivalent: https://google-auth.readthedocs.io/en/latest/reference/google.auth.transport.urllib3.html#google.auth.transport.urllib3.AuthorizedHttp -- I think we should just repurpose that env var to return that instead

[DylanRussell]

requests.Session was added to the constructor of the HTTP exporter 4 years ago: 0590617 - so maybe we want to keep avoid breaking people that might be passing that in ? IDK

[herin049]

requests.Session was added to the constructor of the HTTP exporter 4 years ago: 0590617 - so maybe we want to keep avoid breaking people that might be passing that in ? IDK

The idea is that requests.Session is compatible with the protocol so this isn't actually a breaking change.