[Task] Store existing Discovered Targets in Database

[andrewazores]

Parent: https://github.com/cryostatio/cryostat/issues/937 Depends on https://github.com/cryostatio/cryostat/issues/942

Once we have a database available, the existing target discovery information we have should be stored and retrieved from that database, rather than being done entirely in-memory. Custom Targets should be migrated from storage as JSON files on disk to storage in this database.

[github-actions[bot]]

This PR/issue depends on:

• cryostatio/cryostat#942 By Dependent Issues (🤖). Happy coding!

[andrewazores]

Closed by #1032 / #1028