Allow configuration of custom HTTP headers for agent communication

[jonopryor]

We protect our MeshCentral2 with Cloudflare WAF and Zero Trust.

It would be a huge benefit to be able to configure a custom HTTP header in the agent, so we can further secure our WAF and Zero Trust policy configuration for the agent communication.

Understand this isn't really possible with wss://, so maybe a similar mechanism to the ?key query string that allows a level of control over the web UI would be a viable alternative?