fix(jvmId): correct query for Targets with null jvmId

[andrewazores]

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---

Fixes: #495

Description of the change:

Corrects a database query. Previously it queried with find("id", (String) null), which generates a SQL query like select from Target where jvmId = null and returns no results, even when there are targets with null JVM IDs. The new query is slightly different: select from Target where jvmId is null, with the is null being the significant difference. With this the database query correctly comes back with the targets with a null JVM ID.

https://stackoverflow.com/questions/9581745/sql-is-null-and-null

Motivation for the change:

This fixes the Target persist hook that is responsible for checking if newly stored credentials apply to targets, checking for targets which do not yet have a JVM ID, and then using the new credentials to try to set the target's JVM ID.

How to manually test:

1. Check out and build PR
2. ./smoketest.bash -Ot
3. Go to Topology, confirm that two of the vertx-fib-demo targets have a warning icon and no JVM ID
4. Go to Security and define a new credential: target.alias.contains('andrew'), admin:adminpass123. The CredentialsStored notification should appear, and so should a target update notification for each target
5. Go back to Topology. The two targets should now have no warning icon and should have a JVM ID

[andrewazores]

/build_test

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CI build and push: All tests pass ✅ (JDK17) https://github.com/cryostatio/cryostat3/actions/runs/9388437939