Refactor cog predict to support --json flag (#2404)

* Implement `cog predict --json`

This allows `cog predict` to use JSON as the input/output format which
makes it more suitable for automation such as testing.

* Support writing output file to disk

* Refactor to use same path for output processing

* Cleanup `--output` flag

* Rename write methods

* Always transform outputs

* Clean up display of outputs in cog predict

* Preserve file extensions on `list[Path]` outputs

* Only transform outputs if the prediction was successful

* Exit from `cog predict` with non-zero exit code if prediction fails

* DEBUG

* DEBUG

* Fix adding double file extension

* Fix checking if the extension is an integer

* Add test_predict_json_input integration test

* Add more integration tests

* Support - for stdin input

* Use %q for output name format

* Send error if prediction status fails

* Fix flaky file challenge test

* Fix integration tests

* Remove newline

* Just test output file in output mode

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Co-authored-by: Will Sackfield <[email protected]>

Author: aron