[Epic] Multi-target UI paradigm

Our current UI is very much based around this paradigm of selecting a specific target application and performing actions against that target, or gathering information about that target. This doesn't mesh well with the nature of cloud deployments where we expect Cryostat to be used, where an application is often comprised of many different (micro)services, and where these services can be scaled up to many replicas. We need to design and implement a new UI that allows users to perform actions on many targets at once, or recordings belonging to many targets at once, and we need to find better ways to allow users to perform JFR data comparisons across different targets.

Tasks:
- [ ] https://github.com/cryostatio/cryostat-web/issues/376

Start by reviewing linked issue #376 and the current target-specific UI in cryostat-web. Define the scope for multi-target actions, recordings, and cross-target JFR comparisons; done requires a designed and implemented UI covering those workflows.

Written by the indexing model from the issue text.