Make JSON available via Outputs

[tgorham4]

It can be useful to pass the machine-readable results of a linting run to later CI steps to power customizations like notifications or PR comments

This change requests JSON output from golangci-lint, grabs the results, and makes them available in the action's outputs under the key JSON

[ldez]

Hello,

You can do the same thing by using args: --out-format=json:afile.json.
I think it isn't worth it to always generate JSON reports only for a niche and with other existing solutions.