[Request] Options to use oauth2_proxy on OpenShift

> I think it could be valuable for troubleshooting purposes to be able to force oauth2_proxy use on OpenShift, which seems like it could be done with a similar or the same command line flag too. This way it isn't as directly exposed as a CR field, but it's still an available option. Right now if you're on OpenShift you can only get openshift-oauth-proxy, unless you edit the Operator sources and rebuild from that.

_Originally posted by @andrewazores in https://github.com/cryostatio/cryostat-operator/issues/805#issuecomment-2093512579_

Start by locating the operator's OpenShift-specific proxy selection logic and existing command-line or configuration entry points. Trace how the proxy choice is made, then determine where an override belongs; done means oauth2_proxy can be selected on OpenShift without editing or rebuilding the operator, with coverage for the selection behavior.

Written by the indexing model from the issue text.