Require Relay to use HTTPS

[petruki]

Is your feature request related to a problem? Please describe.
Hosting Switcher API for the public creates breaches as Relay calls are not internally managed by the API.
In this particular situation, we want to require users to provide a valid HTTPS endpoint.

Describe the solution you'd like
Validate the Relay endpoint by requiring it to start with HTTPS.
A configuration can be provided in order to bypass this validation.

RELAY_BYPASS_HTTPS: default false

This flag validation should occur in both situation

• Creating/Updating the Relay endpoint
• Triggering a Relay