fix(notifications): handle labels nested within metadata

[andrewazores]

Related to https://github.com/cryostatio/cryostat/pull/864

[jan-law]

I realized that I configured the frontend label validation to exclude commas and equal signs. We should probably make the validations more lenient to accommodate template=Profiling,type=TARGET:
https://github.com/cryostatio/cryostat-web/blob/main/src/app/CreateRecording/EditRecordingLabels.tsx#L65

[andrewazores]

I realized that I configured the frontend label validation to exclude commas and equal signs. We should probably make the validations more lenient to accommodate template=Profiling,type=TARGET: https://github.com/cryostatio/cryostat-web/blob/main/src/app/CreateRecording/EditRecordingLabels.tsx#L65

I'm thinking maybe we just want to enforce no whitespace. Using a regex like this is also forcing users into the Latin alphabet, and right now they also can't enter labels with a / or other plausibly desirable characters.

That validation should also be enforced on the backend side too, not just in the frontend form. I'll file a separate issue.