chore(jdk): upgrade to JDK21

[andrewazores]

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Depends on #609
Depends on cryostatio/cryostat-reports#275
Depends on cryostatio/jfr-datasource#326
Based on #609
Fixes #364

Description of the change:

This change allows an environment variable to be configured so that...

Motivation for the change:

This change is helpful because users may want to...

How to manually test:

1. Run CRYOSTAT_IMAGE=quay.io... bash smoketest.bash...
2. ...

[github-actions]

This PR/issue depends on:

• build(deps): update Quarkus to 3.8 LTS #609
• chore(jdk): upgrade to JDK21 cryostat-reports#275
• chore(jdk): upgrade to JDK21 jfr-datasource#326
  By Dependent Issues (🤖). Happy coding!

[andrewazores]

/build_test

[github-actions]

Workflow started at 9/30/2024, 11:45:29 AM. View Actions Run.

[github-actions]

CI build and push: At least one test failed ❌
https://github.com/cryostatio/cryostat/actions/runs/11109579821

[andrewazores]

^ failure because the change to update the CI is included in this changeset too, so the CI runner is still trying to use JDK 17 to build and run this, but it requires 21+.