MIME Type and UTI?

We should clarify the MIME Type and UTI that are appropriate for OTIO files.

Currently our documentation says:
```
TODO: Should we specify a MIME Type `application/vnd.pixar.opentimelineio+json` and UTI `com.pixar.opentimelineio` for OTIO, or just use MIME: `application/json` and UTI: `public.json`?
```

What is the right MIME / UTI to use? Is this something we need to register with a standards body?

Start with the documentation TODO quoted in the issue and review the existing comment thread. Research whether OTIO should use the proposed vendor MIME type and UTI or the generic JSON identifiers, including any standards-body registration requirements. Done means the documentation states the selected identifiers and registration guidance clearly.

Written by the indexing model from the issue text.