Support stability definitions from OTEP 232

[lmolkova]

Part of open-telemetry/semantic-conventions#1096

We need to include new maturity levels formally defined in OTEP 232:

• Development - new one that replaces experimental. We should keep supporting experimental, but treat it as developement
• Alpha - new
• Beta - new
• Release Candidate - new
• Stable - no change
• Deprecated - no change (not a stability level from the semconv schema perspective)
• Unmaintained - don't add for now

This would mean:

• extending the stability enum to cover new members
• update is_experimental filter to cover all maturity levels (i.e. return true for all levels except stable)
• update schema definition to list all new possible values

[jerbly]

@lmolkova - I can do this one. Set me as the assignee if you like??

[lmolkova]

@jerbly thank you, really appreciate your help!

[jerbly]

Made #504 - hopefully this is what you had in mind. 🤞