Update to new `gen_ai` semantic conventions from OTel.

[antonpirker]

There where breaking changes in the OpenTelemetry Semantic Conventions for generative AI:

https://github.com/open-telemetry/semantic-conventions/releases/tag/v1.37.0

This should be done after we updated all our existing integration to the semantic conventions we use right now, and after we created the integrations for pydantic-ai and google-genai using the same semantic conventions we use right now.

Updating to the new semantic conventions needs also work in the Sentry UI for the agents insights module, so we need to sync with the telemetry experience team.

There also need to be some changes in relay so the old attribute names are mapped to the new names, so the insights module keeps working with older SDKs sending old attribute names.

See also the DACI to this (employees only)

https://www.notion.so/sentry/DACI-Should-we-follow-the-newest-OTel-convention-for-gen_ai-spans-2648b10e4b5d801d8236ce2d341225b7

[linear]

PY-1826 Update to new OTel SemConv for generative AI.