Implement H264 VideoWritter with gstreamer

[edgarriba]

part of #113

• create a video.rs in kornia-io
• implement VideoWritter and VideoWriterCodec to record h264/rgb videos
• added a new gstreamer error GstreamerFlowError and replaced DowncastAppSinkError by GetElementByNameError.
• create a couple of examples: video_write and video_write_tasks
• clippy fixes in the benchmarks

Output example:

output.mp4