Use/report relative URLs

[andrewazores]

We should investigate if it's possible to remove the various env vars like CRYOSTAT_WEB_HOST, CRYOSTAT_WEB_PORT, CRYOSTAT_SSL_PROXIED - these are all used so that Cryostat can construct authority URLs for itself like https://cryostat.example.com:1234, which are then used to construct URLs for accessing the notifications channel, downloading recordings, or retrieving automated analysis reports. It seems that we should be able to report all of these URLs as simply relative URL paths without the protocol, hostname, port number, and clients should interpret these paths as relative to wherever they are accessing Cryostat from.

This would make the deployment of Cryostat a bit simpler and more flexible.

Also related, can we find a way around having to feed Cryostat the URL for the jfr-datasource and Grafana dashboard?