[FEATURE]-Add support for Presentation ExternalSource features

[cdenig]

Is your feature request related to a problem? Please describe.
It would be very useful for rooms where main control panel is a Cisco to support the Presentation ExternalSource features.

Describe the solution you'd like

• Add External Sources array to configuration.
  • Define info to create ExternalSource on codec.
  • Define Switcher or SourceList elements?
• As part of codec init, ExternalSource RemoveAll and add configured Sources
  • Manual trigger
• Set State of Sources
  • Ready, NotReady, Hidden, Error
  • Source of Truth from SIMPL bridge? from direct fb of switcher?
  • Codec will not display source unless active video (or scaler showing blank screen)
  • Codec will not show active sharing unless active video is ingested by codec
  • NOTE: this cannot be queried, only get a generic StateResult (state=OK) type response
• Add Select Sources from SIMPL event via bridge
  • Example would be to auto-detect video sync in SIMPL and start sharing immediately
  • NOTE: do not send Select on Source_Routed_Fb events. Cisco isn't that smart.
• Add signals to JoinMap so can communicate over a bridge

Describe alternatives you've considered
An alternative would be to use a command passthrough to bridge and let logic and command/response handling occur in SIMPL.

Additional context
Add any other context or screenshots about the feature request here.

[TrevorPayne]

THis is somethign I'm interested in getting added - but it's not been something I've needed.

I say add it :D