Promote cpu.mode attribute and its enum members to release_candidate

[Dipanshusinghh]

Part of #3694

Changees

Promotes the cpu.mode attribute and all of its enum members (user, system, nice, idle, iowait, interrupt, steal, kernel) from development to release_candidate stability status.

this change is a prerequisite for stabilizing container.cpu.time (discussed in #3693), which conditionally requires the cpu.mode attribute.

All markdown tables and documentation have been regenerated using the Weaver tool.

Merge requirement checklist

• CONTRIBUTING.md guidelines followed.
• Change log entry added, according to the guidelines in When to add a changelog entry.
• Links to the prototypes or existing instrumentations (when adding or changing conventions)

[ChrsMark]

LGTM

[Dipanshusinghh]

Hi @open-telemetry/semantic-conventions-maintainers
Could any available maintainer please take a look at this PR when you get a chance?
This promotes the cpu.mode attribute and its enum members from development to release_candidate stability — which is a prerequisite for stabilizing container.cpu.time (tracked in #3693).
The PR already has 2 approvals from reviewers with write access. Just waiting on a maintainer to verify and merge. Thank you!

[lmolkova]

It seems we did not update stability for the attribute when marked metrics that leverage it as RC, this PR fixes that. I'll create an issue to make sure policies are checking for it.