[Task] Devise a trigger condition syntax and implement processing from config about cryostat-agent HOT 5 CLOSED

Here's some info I put elsewhere for another reason, but which I just had the thought could be very relevant here as well:

https://github.com/cryostatio/cryostat/issues/990#issuecomment-1613364915

tl;dr "Common Expression Language" looks like it would be a good syntax for describing smart triggers, and this looks a lot like the JavaScript-based matchExpressions already used by the Cryostat server for Automated Rules and Stored Credentials. This could be used with either Idea 1 or Idea 2 from the original issue I filed here. For Idea 2 I think it is relatively straightforward, an expression or list of expression strings would be passed as part of the Java command line and would become arguments to the agentmain. For Idea 2, the expressions could be provided as the value of a SmallRye Config property, or perhaps a series of properties with a common key format so that multiple expressions can be provided. For the follow-up about using a mounted ConfigMap, this still slots in well, since these CEL expressions can be easily embedded into ex. a YAML document that backs a ConfigMap.

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The idea of using a configuration file for this purpose could also fit with simply defining an optional path to such a file via SmallRye Config property.

In a containers/k8s/OpenShift story, this could be supplied by a ConfigMap:
https://kubernetes.io/docs/tasks/configure-pod-container/configure-pod-configmap/

The ConfigMap can be mounted as a file in the container, and a config property used to tell the agent to load that file to figure out what triggers it should set up.

This same technique can already be used to override the agent's own default microprofile-config.properties, so this idea does also slot in with Idea 1 above in that sense.

If the trigger definition syntax can be expressed in terms of environment variables then the user can either perform this configuration by environment variable or by ConfigMap and embedding the trigger configuration into the existing .properties.

If the trigger syntax cannot be expressed as environment variables or otherwise does not work well with SmallRye Config properties, then a separate config file (ex. ConfigMap) defined in some other format such as JSON/YAML could be used.

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@Josh-Matsuoka ^

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Sounds like a good approach to me, I'll do some reading/look into it!

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Done in #197

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