Adds mistralai as a gen_ai.system attribute value

[codefromthecrypt]

This extends GenAI System to include Mistral AI. This accessed either via its native 'mistralai' API or via OpenAI libraries.

This is a follow-up to #1655

Changes

Added the following:

• "mistralai", not "mistral" as their client library is named "mistralai", despite some of their models named "mistral-XXX"

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.

[drewby]

This addition looks good to me.

[lmolkova]

since it's spelled as two words in the docs and on the trademark I believe it should be

Suggested change

	- id: mistralai
	- id: mistral_ai

[codefromthecrypt]

so in the README I wrote this:

"mistralai", not "mistral" as their client library is named "mistralai", despite some of their models named "mistral-XXX"

do we want to use a convention different than what they are using? ok by me, but worth the question.

[codefromthecrypt]

@Bam4d since you are from mistral, maybe you can answer this question. OpenTelemetry will make signals like metrics, and a dimension of the metrics is where chat requests are coming from. For Mistral AI, should the string be "mistralai" or "mistral_ai" (or something else). We just want to use a coherent value and there are multiple seemingly correct choices.

Thanks for letting us randomly ping you.