Split DBus Auth Manager interface into two parts

Acceptance criteria:

• Implement a new DBus endpoint io.mender.Proxy1.SetupServerURLProxy, under object io.mender.Proxy and path /io/mender/Proxy.
  • It takes two string arguments, the JWT token and server URL, for example: mytoken and https://hosted.mender.io/
  • It returns one string, a localhost address, for example: http://localhost:54321
• What it does is to reconfigure the proxy from MEN-5013 to start serving the submitted ServerURL.
• The returned proxied address is a singleton, in other words, each time the DBus endpoint is called, a new port is opened and the old one is torn down (existing in-progress connections should be allowed to finish).
• The new endpoint must be documented in io.mender.Proxy1.xml.
• Add io.mender.Proxy1.xml to Makefile.

This means that collaberation is needed while also implementing MEN-5013.