feat(names) add --format option

[DanielDewberry]

Add --format option to snapcraft names to enable output format selection. Possible choices are:

• table (default, existing behaviour)
• json

tests/unit/commands/test_names.py:

• Add test class TestNames.

• Rename test_names to test_table and move it into the scope of TestName. Add format to argparse.Namespace.

• Add test_json to TestNames.

• Have you followed the guidelines for contributing?

• Have you signed the CLA?

• Have you successfully run tox run -m lint?

• Have you successfully run tox run -e test-py310? (supported versions: py39, py310, py311, py312)

---

The motivation for adding JSON formatted output to the names sub-command, is that of data pipelines. It will enable tooling to read the command output and leverage JSON parsers rather than performing text processing. A small quality of life improvement :)
The JSON structure leaves room for extension if subsequently required:

{
    "snaps": [
        {
            "name": "test-snap-private",
            "since": "2016-07-26T20:18:32Z",
            "visibility": "private",
            "notes": "-",
        },
    ]
}

[DanielDewberry]

I added the email address on the commits to Launchpad several hours ago in the hope that the CLA check would validate correctly...

Update: I have subsequently signed the CLA again to see if the database will store it now that the email address is in Launchpad

[mr-cal]

Great work, thanks for another contribution!

[lengau]

Thanks! This looks fairly similar to how Charmcraft does this, but with some improvements I'll probably be copying over :-)

[lengau]

@DanielDewberry if you have opinions on a general case for this on more commands (e.g. list-tracks), I'd love to hear them in this feature request.

[DanielDewberry]

Thanks! This looks fairly similar to how Charmcraft does this, but with some improvements I'll probably be copying over :-)

Thank you, that's a compliment and a half :)