⬆️ Add gstnvcodec support to videnc

Finalize work around videnc quiddity to be able to use either x264enc or nvcudah264enc from GStreamer 1.22.

• Allow to load any GStreamer encoder elements, even them that have no primary/secondary rank. This is necessary to access nvcudah264enc.
• Set sane defaults for x264 and nvcudah264enc for videoconferencing.
• Default all encoders to 2 Mbps bit-rate.
• Make sure all h.264 encoder respect main profile. This fixes cases where x264 would send 4:4:4 because of high profile precedence on pad caps.
• Automatically prefer hardware codec when available.
• Use codec short name in codecs property.
• Refactor video codecs initialization to allow loading them by their short name in a bundle.
• Export codec field in shmdatasink caps so Scenic can display which encoder is used.
• Treat selecting codec id 0 as resetting, this is workaround because Scenic does not invoke reset method.
• Remove extra thread (queue) between shmdatasrc and videoconvert.
• Remove videoconvert n-threads option, this reduces tearing effect observed when bundling videnc with videoconvert quiddity.
• Remove custom nvenc quiddity along with all its documentation and build dependencies.