Add CR property to disable Cryostat built-in discovery mechanisms

[andrewazores]

The environment variable CRYOSTAT_DISABLE_BUILTIN_DISCOVERY can be set to true on the Cryostat container to disable the built-in discovery mechanisms. In an Operator context this would mean disabling Cryostat's Endpoints querying/watch. This would be used in cases where the end user only intends to have applications discovered via the Discovery Plugin API.

[tthvo]

@andrewazores I just noticed that Cryostat check the presence/non-blankness of the variable to determine whether to disable built-in discovery.

https://github.com/cryostatio/cryostat/blob/bc9eb4d2319eb8e2b340eca6090fdc41c176e162/src/main/java/io/cryostat/discovery/BuiltInDiscovery.java#L82

Should this condition also includes a check for its value? If not, the operator can just not mount the environment in if disabled option is chosen.

[andrewazores]

It could be a check for the value, sure. But I think in a few different places Cryostat just does what you see there and checks whether the variable is defined/non-empty, rather than checking for a specific "true" string.

Is how it works now easy enough to deal with on the Operator side?

[tthvo]

Right, it would not be a problem :D Operator could check and not mount the environment easy enough.