Add support for tcp:// DOCKER_HOST

The Docker daemon that I am using is running remotely, and I connect to
it via Tailscale tunnel, which means that my DOCKER_HOST is set to
tcp://100.113.182.91:2375

This change makes Dagger work with my setup. It's been running well for
me for a few weeks now, this started as https://github.com/thechangelog/changelog.com/pull/395

I think there is an opportunity to add support for ssh:// & file://,
but I am keeping this first addition small on purpose.

Signed-off-by: Gerhard Lazu <gerhard@lazu.co.uk>
Signed-off-by: Sam Alba <samalba@users.noreply.github.com>

stdlib/docker/tests/command-host/command.cue

@@ -0,0 +1,17 @@
+package docker
+
+import (
+	"alpha.dagger.io/dagger"
+)
+
+TestConfig: {
+	host: string @dagger(input)
+}
+
+TestHost: client: #Command & {
+	command: #"""
+			docker $CMD
+		"""#
+	host: TestConfig.host
+	env: CMD: "version"
+}