Python library for OpenTelemetry-proto based on python-betterproto

See https://github.com/open-telemetry/opentelemetry-proto and https://github.com/danielgtaylor/python-betterproto

Easiest way to (re)generate is to

• make sure the opentelemetry-proto submodule is updated git submodule update.
• run the makefile with the necessary dev dependencies, easiest with uv run make assuming uv is installed.