fix: video_channel ownership #1511

[Julusian]

There is some bad ownership handling of the channels. When creating amcp_command_repository it holds a copy of the pointer for each channel.
This class is not being destroyed correctly, because the main loop holds a reference for the console amcp client, causing it to not be destoyed when expected.

This then crashes because once caspar thinks it has destroyed everything, it tells cef to shutdown which causes the crash as the renderers are still active (as are all the channels, producers and consumers).

This fixes that by swapping out the root channels vector to contain the type needed by amcp_command_repository, which avoids the ownership issues