This fixes issues in the swagger.json file. The motivation to do so is to be able to generate API clients using https://openapi-generator.tech Doing so will require further changes to the api spec, but this seems like a good first step since it is now "valid" according to editor.swagger.io and openapi-generator validate.
Fixes#2806
- API to fetch info of a single inbox
- Document passing custom_attributes in the API
- Ability to filter contacts with contact identifier in search API
