Add support to protobuf6 and regenerate proto files

[emdneto]

Description

Drop support for Protobuf 5 Regenerate proto files using libprotoc 31.1 Update tests to use protobuf==6.31.1, grpcio=1.73.0 and googleapis-common-protos==1.70.0 Require grpcio >= 1.73.0 for exporter-otlp-grpc

Fixes #4639

Type of change

[!IMPORTANT]

• [X] Breaking change: Users stuck on protobuf <6 cannot:
• Get newer minor versions of the SDK (1.36.x, 1.37.x, etc.)
• Receive API/SDK updates beyond 1.35
• Use newer exporter versions that might have bug fixes or features

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

• [X] Tox tests in CI

Does This PR Require a Contrib Repo Change?

• [ ] Yes. - Link to PR:
• [X] No.

Checklist:

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