[Story] Declarative Stored Credentials

[andrewazores]

See #726 for Event Templates example. It should be possible for users to provide files containing Stored Credentials definitions under some directory, and Cryostat should attempt to load these into the Stored Credentials database on startup. These files should probably be JSON, like:

{
  "username": "user",
  "password": "somepassword",
  "matchExpression": "true"
 }

In Kubernetes, these would be supplied by mounting Secrets to the container.

• [Task] Declarative Stored Credentials #728
• [Task] Declarative Stored Credentials cryostat-operator#978
• [Task] Declarative Stored Credentials cryostat-helm#218