Add a `launch` command

[nickchomey]

It would be great if there was a ddev spx launch command available, which would open a browser tab to https://example.ddev.site/?SPX_KEY=dev&SPX_UI_URI=/

[GuySartorelli]

One way to do this would be to take the logic that's currently in the spx web command and move that into a web-build/spx-functionality (or similarly named) file.

Then remove the web command, and replace it with a host command called spx.

If the argument passed to ddev spx is "launch", run ddev launch "?SPX_KEY=dev&SPX_UI_URI=/".
For all other arguments, run ddev exec spx-functionality "$@" which will do all the logic the current web command does.

I'd be happy to implement this, but given the existing PRs haven't had so much as a comment I'm hesitant to do so without some assurance it'll be looked at by the maintainer.