oxfmt: allow trailing commas in `.oxfmtrc.jsonc`

[jasperteo]

It is common for formatters like Prettier to automatically add trailing commas to json/jsonc files.

The current schema does not allow for trailing commas, resulting in text editors linting it as an error.
https://github.com/oxc-project/oxc/blob/main/npm/oxfmt/configuration_schema.json

Can modify the schema with an additional property to allow for trailing commas

{
  "allowTrailingCommas": true,
}

[leaysgur]

Will be fixed in #15612.