pytrickle: enable encoder setup to be configurable

[eliteprox]

Add ability in pytrickle to configure the encoder metadata.

Current configuration

• Decoder configures the encoder based on the input stream
• Generative streams use a default_output_metadata to setup the encoder.
  • Limited configurability
    • max_framerate, height and width passed stream start request will limit the framerate of the encoder

Wanted:

• Accept a json object to set the metadata in whatever way is wanted.

[linear]

COMFY-268