rootless: update for v20.10.6
rootless: update for v20.10.6

- btrfs is now supported (moby/moby PR 42253)
- CLI context "rootless" is now created by default (moby/moby PR 42109)

Signed-off-by: Akihiro Suda <10ddef0dea2a66ab193b07198faa879adcb213d8@hco.ntt.co.jp>

thaJeztah/docker.github.io,docker/docker.github.io,thaJeztah/docker.github.io,thaJeztah/docker.github.io,docker/docker.github.io,thaJeztah/docker.github.io,docker/docker.github.io,docker/docker.github.io,docker/docker.github.io,thaJeztah/docker.github.io