Merge experimental and stable attributes per resource type.

[jsuereth]

Merge the experimental and stable portions of resource together where previously we had them split by group but still had them with the same type.

Marking this draft to get review on direction.

My own concern is around whether the notion of "stable resource type" but "unstable attributes" is clear or needs called out somewhere else.

Changes

• Merge service experimental + stable attributes in the same group.
• Merge telemetry.sdk experimental + stable attributes in the same group.
• Modify markdown so that both stable + experimental attributes show up joined for a given resource type.

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.