Document and encode proxy setup procedure

[kreczko]

1. Add documentation to docs/dev.rst on proxy setup and selection of DIRAC instance
2. add dask-dirac login <dirac URL> -g <group> command to
   a. setup dirac instance (checking for existing config)
   b. create proxy for specified group (printout location of created proxy + useful info, make sure to use typer.prompt with hide_input=True)
   c. check validity by running whoami against the target DIRAC server

Probably worth adding a WARNING: This step requires DIRAC installation (for now).
Once we have a good recipe, we can probably replace installation with a docker image to get the proxy - this would be similar to the recipe on how to get a scitoken.

[seriksen]

Documentation for the proxy setup for diracdev server and cert server is in the servers.rst on se_dev branch