Make switch easier with flags instead of positionals

[thekaveman]

Current

Right now the switch command works like:

$ littlepay switch --help
usage: littlepay switch [-h] TYPE VALUE

positional arguments:
  TYPE        The type of object to switch
  VALUE       The new object value

options:
  -h, --help  show this help message and exit

E.g. to switch the environment to qa:

littlepay switch env qa

Proposal

It would be nicer to use flags instead of a positional for the TYPE argument:

littlepay switch --env qa

This would allow for e.g. shortcut flags (particularly helpful for the participant type):

littlepay switch -p cst

And even switching both env and participant at the same time:

littlepay switch -e qa -p cst