[Story] Unsupported features when using a readonly Cryostat Agent should display nice warnings/errors

[andrewazores]

The Cryostat Agent currently provides only a readonly implementation mirroring some of the actions that Cryostat can perform on JVMs over JMX. In cases where the user tries to do something unsupported, like dynamically starting a new recording, the error message displayed should be informative and helpful.

• [Task] "Create Recording" displays an unhelpful error view when performed on an HTTP Agent #944

[andrewazores]

Done: #944