feat(recordings): Add recording metadata labels

[jan-law]

Related #709
Depends on cryostatio/cryostat-web#383

Adds a patch handler and helper functions to optionally add labels when starting a recording on a target. The patch handler is used for editing labels for existing active or archived recordings.

[andrewazores]

Looks great overall, thanks for all this! Other than the small details I've left comments about, I have one higher-level internal implementation detail concern here. It seems that the API is defined to accept the labels as a string, but that string must be a JSON object/map. But, internally, the labels are passed around as the raw String, and when included in an API response (as a serialized recording descriptor), the labels field is actually again simply a String that has contents that appear to be JSON - but it will be wrapped in double quotes in the response as a String, not an actual JSON object.

I think it would be best to parse the client's request body as JSON right away in the handlers/manager, expecting it to be mappable to a Java Map<String, String>. If it isn't then that is a 400 response. If it does, then the labels object that is passed around internally should be the Map, and this is also what should be kept as a field reference in the serializable recording descriptor. This can still be serialized to JSON for storage on disk, and when included as an API response as a serialized recording descriptor, it will be nicely embedded as a JSON object/map rather than a String that looks like further encoded JSON.

[andrewazores]

Code looks good. Could you update HTTP_API.md?

[andrewazores]

rebase please

[jan-law]

Latest build failure caused by No recording data available in ArchivedReportJwtDownloadIT. This test is passing locally.

testDownloadRecordingUsingJwt  Time elapsed: 11.602 s  <<< ERROR!
java.util.concurrent.ExecutionException: java.lang.Exception: HTTP 500
	at itest.ArchivedReportJwtDownloadIT.testDownloadRecordingUsingJwt(ArchivedReportJwtDownloadIT.java:78)
Caused by: java.lang.Exception: HTTP 500

INFO: (10.0.2.100:58684): PATCH /api/v1/targets//service:jmx:rmi:%2F%2F%2Fjndi%2Frmi:%2F%2Fcryostat-itests:9091%2Fjmxrmi/recordings/someRecording 204 241ms
Mar 09, 2022 9:09:52 PM io.cryostat.core.log.Logger error
SEVERE: HTTP 500: io.cryostat.recordings.EmptyRecordingException: java.io.IOException: java.io.IOException: No recording data available
io.vertx.ext.web.handler.impl.HttpStatusException: Internal Server Error
Caused by: java.util.concurrent.ExecutionException: io.cryostat.recordings.EmptyRecordingException: java.io.IOException: java.io.IOException: No recording data available