Ability to specificy which json file to use instead of test_input.json

[captainjapeng]

Is your feature request related to a problem? Please describe.
When testing locally, Serverless only accepts a string input via --test-input or via test_input.json. A task may have different input fields depending on the desired output so we have to keep modifying test_input.json to test specific behaviors.

Describe the solution you'd like
It would be nice we there's a way to point to a specific json file to use using the command line like --test-file other.json.

Describe alternatives you've considered

Additional context