Notify on schema push if no schema files are found

[henryfauna]

Ticket(s): FE-6218

Problem

schema push will let you nuke your schema if you accidentally specify the wrong directory with no .fsl files.

Solution

In order to run schema push you must specify a directory with .fsl files.

Result

You can't run fauna schema push --dir /wrong/dir --no-input and nuke your schema.

Testing

Added a test.

[ecooper]

Do we think this is a validationerror? Should we throw that?

The schema commands are interactive by design so I'm torn.

[henryfauna]

Do we think this is a validationerror? Should we throw that?

The schema commands are interactive by design so I'm torn.

Yeah I think an error makes sense here. It would be nice to not fail silently if you were running schema push --no-input from a script or something.