Complete roundtrip of PL <--> OPB MD conversion

[Bluesy1]

Complete the PL to/from OPB MD roundtrip

TODO:

• Add support for asset files
• Reorganize new imports to their own section instead of at the top of the import list
• Add parameter for output destination and write file(s) generated to destination
  • Also copy back asset files
• Add test cases (expected outputs -> markdown files)
• Update test action to upload generated return trip outputs
• Add documentation elsewhere in the file to note cases when new features are added will require the parts of the parser to be updated to match compatibility
• Add support for keys that cannot be roundtripped (waiting on progress on Finish the roundtrip: PL --> MD conversions #86 for this)

Resolves #86

[Bluesy1]

Benchmark of what output looks like as of August 11th, 2023: https://gist.github.com/Bluesy1/6f497bc1ed5b4a3aae25f91918abe2ad

[Bluesy1]

For now, to make the roundtrip possible, I've shoved all the extra keys I can't get normally into a nested object inside the comment section of the info.json generated files to at least see how that would look - I'm happy to change and/or modify the method if needed, or just accept that those sections have to be manually copied back (reverted to prior state?), by a human.

I expect this will need multiple rounds of review since its a fairly large change, but it should be mostly feature complete now and working.