Check attribute/metric/event name format

[lmolkova]

Fixes #1124

Changes

• adds checks for attribute, metrics, and event name format
• adds a note to the attribute naming about current tooling limitations

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.

[MadVikingGod]

Is there a check for the group.id?

Other then that looks good.

[lmolkova]

Is there a check for the group.id?

great point! No check yet, I added it to open-telemetry/weaver#306 - this PR focuses on attributes

[jsuereth]

@lmolkova I'm merged, and now there's conflicts here... apoligies.