[Request] Agent should require TLS connection to server by default

[andrewazores]

The Agent should check its baseuri property that points to the Cryostat server with which it should register. By default, the Agent should enforce that this URI uses an https scheme, and when the Agent opens a connection, it should expect that it really does find an HTTPS connection, with a TLS certificate that it trusts, etc.

It should be possible to disable this and allow insecure HTTP (mainly for testing/prototyping purposes), but this should be controlled by a new and separate configuration property.