Use // comments for .json

[injust]

Add comments to .json files using // instead of the default #.

Even though JSON does not support comments, JSON5 and JSONC exist, so // is a much more sane default. It also improves the experience of editing micro's own config files.

[plutonium-239]

Thanks, hoping this gets merged soon

[JoeKar]

From my perspective it's good to chain the default from # to // in case the comment plugin is used within json.
But the user has to keep in mind, that he can add potential issues to JSONs which aren't parsed with json5 or jsonc. Since before a # was added it's most probably not a big deal and adds at least the correct comment type for newer JSONs.