Change azure_ to az. in cloud.platform enum values

[lmolkova]

Azure-specific attributes/signals use az. prefix to denote they belong to az namespace:

• https://github.com/open-telemetry/semantic-conventions/blob/main/docs/attributes-registry/azure.md
  • those are actually used by stable libraries and should be declared stable (so az vs azure ship has sailed)
• https://github.com/open-telemetry/semantic-conventions/blob/main/docs/azure/events.md

We also use az. prefix/namespace in az.ai.inference (gen.ai.system enum value)

I'd like to try and consolidate cloud.platform enum values.

TODO: check with other MS folks and check existing usages to see how breaking it would be:

• azure_aks -> az.aks
• azure_app_service -> az.app_service
• azure_container_apps -> az.container_apps
• azure_container_instances -> az.container_instances
• azure_functions -> az.functions
• azure_openshift -> az.openshift
• azure_vm -> az.vm

Related to #1684 (comment), #608

PS: I'd encourage similar renames for AWS and GCP, but I have no means to check how much pain it would cause.

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.

[lmolkova]

/cc @trask, @mattmccleary, @rajkumar-rangaraj, @cijothomas, @lzchen @RohitRanjanMS, @OsvaldoRosado, @reyang if the have any context on how breaking they expect it to be.

[RohitRanjanMS]

Thanks, @lmolkova . Functions is still in its early stages with respect to OTel, and I don't see any issues with this proposal.

[lzchen]

We do have azure resource detector that use some of these values although the component itself is experimental. In azmon exporter, we currently do not map resource attributes to telemetry custom dimensions BUT we do populate OTELRESOURCE custom metric which is populated with the resource attribute information. I believe this feature is in preview as well so probably not an issue to make breaking changes.

@jeremydvoss