feat: new output.formats file configuration syntax

[ldez]

This PR improves the syntax inside the configuration file to specify output formats.

The previous syntax has been defined when only the format type was an option.
However, the syntax has evolved to support output paths and multiple formats.

output:
  format: "checkstyle:report.xml,json:stdout,colored-line-number"

This is a flag syntax friendly but not a file syntax friendly.

I propose this new syntax:

output:
  formats:
    - format: checkstyle
      path: report.xml
    - format: json
      path: stdout
    - format: colored-line-number

The CLI flag keeps the same syntax.

--out-format=checkstyle:report.xml,json:stdout,colored-line-number

To keep this new option compatible with the GitHub Action, the CLI must override the configuration file.

The previous field output.format is deprecated and works as before but with a warning.

[Antonboom]

👍