[CCAP-629][CCAP-575] Support for converting documents and images to pdfs

[cram-cfa]

Issue tracking number 🔗

https://codeforamerica.atlassian.net/browse/CCAP-629

Description of change ✍️

Priority 🥇

Effect on other applications using FFB 🌊

Testing

✅ Checklist before requesting a review

• Does the new code follow our preferred coding
  style?
• Does the code include javadocs, where necessary?
• Have tests for this feature been added / updated?
• Has the readme been updated?

[analoo]

The only part that is still unclear to me is where the conversionSourceFileId is set.

[cram-cfa]

This is generated on line 191; It is the UUID of the entry for the file that was uploaded by the user. It has to be generated in the code -- and not by the database -- so we can properly set the path on the uploaded file. (This was actually a bug before, but since we don't really care what the path is, as long as it's set... it's not actually causing any issues in production, etc)

Once the uploaded file has a UUID, we want the new converted file to have a reference back to that uploaded file -- hence it being the "conversion source file's id".

The code to create the UUID previously was way up at the top of the method, I just moved it to line 191 where it is first ever needed.

Let me know if that explains it!