[RFE] Build and ship Docker sysext

[t-lo]

Current situation

Docker is shipped via Torcx.

Impact

Shipping Docker with torcx increases boot time (docker tarball needs to be decompressed) and memory usage at runtime (torcx uses a tmpfs for docker binaries). Torcx is deprecated and in maintenance mode, posing a potential security risk.

Ideal future situation

Docker is build as a sysext and included in the base OS image (and update tarball).

Additional information

This issue depends on #1091 and requires #1093 to be implemented to be feature complete (end-end-dependency).

@krishjainx wanted to look into this.

[krishjainx]

Can work on this once flatcar/scripts#920 is merged