Allow JSON input in CLI

[TheJolman]

this would make testing with pre-written payloads that need to go through the oauth flow much faster. Payloads should be the same as the models that API accepts.

Potential usage/examples:

# Option 1
acmcsuf-cli events post < payload.json

# this would also be supported
acmcsuf-cli events post <<EOF
'{"name": "bobby b", "github": "bobby_b"}'
EOF

# and this maybe?
echo '{"name": "bobby b", "github": "bobby_b"}' | acmcsuf-cli events post

# Option 2
acmcsuf-cli events post --json payload.json

I'm slightly partial to option 1 since I'm used to xh behaving that way, but either would be useful. Both could be implemented as well.