Remove hardcoded `docker` CLI command name for SSH hosts

[mattmacleod]

Description

Currently, when connecting to a remote SSH host, the docker binary name is hard-coded.. This means that if the remote host doesn't have a binary named docker in the path, remote SSH support doesn't work.

There are two specific use-cases this makes difficult:

• Systems where docker isn't in the path for the SSH connection, and
• Systems where the docker binary has another name.

If this hard-coded default could be overridden, these use-cases could be supported.

Proposal

Introduce the DOCKER_SSH_REMOTE_BINARY environment variable, which will be used in place of the bare docker binary if set. I'll raise a PR for this change then link to it.

Associated PR: #5627

Related

Would resolve #3045