Ports project volume cleanup from docksal#1058

[lpeabody]

Changes

• All project_root named volumes were leftover after proxyctl cleanup ran, even for projects that no longer exist. After discussing with @lmakarov, backporting the change in https://github.com/docksal/docksal/pull/1058/files#diff-41adca34c3eac75ca9453c7cb0634f6aR1285 makes sense to have here.

[lpeabody]

Alternatively, we could replace:

	log "Removing dangling volumes..."
	docker volume prune -f

with:

	log "Removing dangling volumes..."
	docker volume ls -qf dangling=true | xargs -r docker volume rm

[lmakarov]

We cannot use docker volume ls -qf dangling=true | xargs -r docker volume rm due to docksal/docksal#1056. It can only be used as a one-time fix if you know what you are doing.