[PTDT-3002] SDK updates for PDF connections

[kvilon]

Description

Please include a summary of the changes and the related issue. Please also include relevant motivation and context.

Test cases

• Relationship with a source, but not source_ontology_name - should work correctly
• Relationship with a source_ontology_name, but not source - should work correctly
• Relationship with both source and source_ontology_name - throws an error, only one of them can be defined
• Relationship without both source and source_ontology_name - throws an error, at least one of them should be defined
• readonly field - can be True of False
• Should support all 3 types of classifications (radio, checklist, text)
• Should support both bounding boxes and text entities
• Can import using python annotation classes
• Can import using NDJSON

[Jmsa]

PAT & LGTM

[kvilon]

All tests pass locally (unit, integration, data).