Add tests of --pretty option for get, cancel, wait, create, request commands of Data CLI

[sgillies]

Discovered in https://github.com/planetlabs/planet-client-python/projects/2#card-81309600.

[jreiberkyle]

The underlying logic is tested in a unit test for echo_json (here). Therefore, the only piece that isn't being tested is whether the pretty option is indeed passed to echo_json. This can be a very simple and copy/paste type of test where echo_json is mocked and the test checks to see if it got called with the pretty option as expected.

I am absolutely pro doing this and also I wouldn't triage this as high priority given the simplicity of the logic it tests.