Write a formatter utility

[FichteFoll]

The formatter should:

• Unify labels and translate them to lower case (Clean up labels a bit and see if contributions here are welcome. #4277)
• Unify repository urls and remove trailing slahes for example
• Remove redundant keys that would be equivalent to what PC finds from details, notably readme, author, base
• Remove redundant keys that specify the general default value, notably platforms (also "platforms": ["windows", "linux", "osx"])
• Unify whitespace usage. I'm thinking of what example-repository.json uses, which is:
  • Block style by default, that means a new line for each value
  • Inline style (in same line) for labels, author and platforms keys
  • The same indentation/whitespace style (I don't think I need to explain this)
  • No trailing whitespaces
  • Newline at EOF
• -(Optional) Add a name key for github repos if none present? We could make this a soft requirement in the process.
• Transform all platforms values into a list?

More?

[joshgoebel]

Seems reasonable... are contributors going to be the ones required to run this tool after making any changes or adding a plugin? Not sure we want to make that process any more difficult for newcomers.

[FichteFoll]

No, I don't think we can reasonably require package authors to run it, but it will be a part of the ChannelRepositoryTools package so that they can do it optionally. There doesn't seem to be a reasonable way to include this in the travis ci build either.
I mainly intend this to be a "run once in a while" thing for maintainers.

[twolfson]

For Travis CI, we might be able to run the formatter then diff to see if there are changes/not. If there are changes (i.e. formatter wasn't run since last commit), then we could complain and exit with a non-zero code.

[robfrawley]

@twolfson +1

[FichteFoll]

Some of the formatter features have been added as tests in #7853, so the user can fix the issue by themselves.

[FichteFoll]

Better idea: We can have a github action run the formatter on pull requests and push to the branch when there are changes and run the tests afterwards, also via actions instead of travis.