Update data structures and file upload processing to support `ipa` extension

[lukeheath]

Task

Update Go data structures and file upload processing to support ipa extension and parse necessary metadata.

Condition of satisfaction

ipa file extensions are uploaded and metadata is correctly parsed and inserted into the database.

Notes

• One of our plist parsing libs handles binary plists: https://www.howett.net/projects/plist/
• See comment on API design PR for metadata requirements.