Extend GenAI system well-known values

[TaoChenOSU]

Add more well-known GenAI model providers to the list of possible values that the gen_ai.system attribute can take.

Changes

The following are added:

• microsoft
• huggingface
• google
• meta
• anthropic
• mistral
• cohere

Note: if the PR is touching an area that is not listed in the existing areas, or the area does not have sufficient domain experts coverage, the PR might be tagged as experts needed and move slowly until experts are identified.

Merge requirement checklist

• CONTRIBUTING.md guidelines followed.
• Change log entry added, according to the guidelines in When to add a changelog entry.
  • If your PR does not need a change log, start the PR title with [chore]
• schema-next.yaml updated with changes to existing conventions.

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: TaoChenOSU / name: Tao Chen (469bcb3, 27c9669, 123ed4e, 6b59f94, 6074e1c)

[TaoChenOSU]

I think HuggingFace will be the most controversial one. It's neither a model provider nor a service provider. You can use its inference endpoint but for production people may use their dedicated endpoints, which can be hosted on Azure, AWS or GCP.

[TaoChenOSU]

I removed some of the most controversial values. The remaining ones are known to have client SDKs.