Embed youtube videos into relevant docs

[rothgar]

Some examples

Service proxy - https://youtu.be/N9qpCcxzPlI
Image cache - https://youtu.be/Ir2m11Cijas
Overlays - https://youtu.be/3jF8qyBkdEs
Tailscale extension - https://youtu.be/wjDtoe-CYoI
Talos dashboard - https://youtu.be/52Wmkb0H-98
Infra providers - https://youtu.be/h1eVe-i__pc