Add handling of emqx and verdaccio for local testing

A full FF install requires emqx and verdaccio to be running locally with particular configurations.

We have [docs for setting up verdaccio](https://github.com/FlowFuse/website/pull/3010) (with the custom auth plugin), but not for emqx.

It would be best if the dev-env provided a simple one-command way of setting them both up.

### EMQX

- Assume docker is available (fail gracefully if not)
- copy the default config files in place
- provide start script to run
- include docs on how to customise the setup if other ports are needed etc

### Verdaccio

ref https://github.com/FlowFuse/website/pull/3010

- Add the auth plugin to the list of repos dev env includes
- Create working dir for verdaccio
- Build and install auth plugin
- provide start script to run
- include docs on how to customise the setup if other ports are needed etc