Running stac-client with no arguments should give defined error and usage rather than exception

[philvarner]

I ran stac-client with no arguments, and got the following:

$ stac-client
Traceback (most recent call last):
  File "/Users/philvarner/.local/share/virtualenvs/stac-api-validation-suite-tzI1nfla/bin/stac-client", line 8, in <module>
    sys.exit(cli())
  File "/Users/philvarner/.local/share/virtualenvs/stac-api-validation-suite-tzI1nfla/lib/python3.9/site-packages/pystac_client/cli.py", line 127, in cli
    loglevel = args.pop('logging')
KeyError: 'logging'