feat(jmcagent): add API handlers for JMC agent plugin

[Josh-Matsuoka]

Fixes #577
Fixes #578
Fixes #579

This PR adds jmc agent support to cryostat through a set of API handlers for managing probe templates (xml files detailing the desired transformations) as well as interacting with the agent (adding, removing, retrieving currently active event probes). Accompanying tests have been added. The CI failures should be resolved once the core support (cryostatio/cryostat-core#103) is integrated in core.

[andrewazores]

Please rebase.

This will also need an update to pom.xml to use cryostat-core version 2.4.0 once it is tagged and released, as this will be the minor version update that includes the corresponding JMC Agent plugin classes. cryostatio/cryostat-core#104

[andrewazores]

Not sure what that itest CI failure is exactly - some brief googling suggests that exit status 124 indicates that the command timed out. @Josh-Matsuoka could you also rebase this again?

[Josh-Matsuoka]

@andrewazores I've fixed the issue that was causing the itest container to fail to run, the current build failure is

ReportJwtDownloadIT.testDownloadRecordingUsingJwt:72

which fails on a clean version of cryostat for me as well and seems to be unrelated to this PR.

[andrewazores]

@Josh-Matsuoka please file a new issue for this test failure if there isn't one already, and include logs from both the frontend Maven test runner as well as the backend logs (target/cryostat-itest-sometimestamp.log, or the print itest logs task in the CI run)

[andrewazores]

@Josh-Matsuoka rebase please

[andrewazores]

@Josh-Matsuoka please file a new issue for this test failure if there isn't one already, and include logs from both the frontend Maven test runner as well as the backend logs (target/cryostat-itest-sometimestamp.log, or the print itest logs task in the CI run)

https://github.com/cryostatio/cryostat/runs/4461031558?check_suite_focus=true#step:9:1392

Looks like this is #666, so it is indeed unrelated to this PR and has already been filed.

[andrewazores]

CI is currently failing due to spotless formatting violation

[andrewazores]

Looks good other than the sanity check RuntimeException thing.