src: Get video formats using Device Monitor

[joaoantoniocardoso]

update 09/29/25:

This seems very promising -- so far, I have already replaced the v4l formats and the v4l device discovery.

I'm thinking we should refactor the source/pipeline part of the application to fully make use of this Device Monitor:

1. I still need to reason about the architecture, but I think we can safely say that at least we should split our "Pipelines" (v4l2_pipeline.rs, etc) into a source (pipeline: source -> capsfilter -> parser -> proxysink) + transcoding pipeline (pipeline: proxysrc -> video_tee -> rtp_payloader -> capsfilter -> rtp_tee, as well as the future optional decoder+encoder), which will then connect to our many sink (pipeline: proxysrc -> sink).
2. Then we create a Device enum (w/ VideoSource and AudioSource variants) and a DeviceProvider trait, implemented by both this GSTDeviceMonitor and by the OnvifDiscovery, to give us a common interface.
3. Each "gst::Device" is also an element factory provider, which allows you to create its source element with no effort, which will help us to more easily reach libcamera and audio support.

Helps #139, #372, #79