Video Server Rebranding

[phreed]

The video-server used by FTH was rebranded in v0.22.2 https://github.com/bluenviron/mediamtx/releases/tag/v0.22.2.

The new name is MediaMTX.

This caused changes in the naming convention used in:

• URL : https://github.com/bluenviron/mediamtx/releases/tag/v0.22.2
• Artifacts : https://github.com/bluenviron/mediamtx/releases/download/v0.22.2/mediamtx_v0.22.2_linux_armv7.tar.gz
• files : mediamtx.yml

Update documentation and installers to reflect these changes.

Note: the service has a blocking issue #2