Fix issues with document endpoints being too restrictive

[diversemix]

Description

Various properties of the pydantic response definition were too restrictive - not allowing for NULLs

Background

From the schema:

                     Table "public.family_document"
        Column        |      Type      | Collation | Nullable | Default 
----------------------+----------------+-----------+----------+---------
 family_import_id     | text           |           | not null | 
 physical_document_id | integer        |           | not null | 
 import_id            | text           |           | not null | 
 variant_name         | text           |           |          | 
 document_status      | documentstatus |           | not null | 
 document_type        | text           |           |          | 
 document_role        | text           |           |          | 

                               Table "public.physical_document"
    Column    |  Type   | Collation | Nullable |                    Default                    
--------------+---------+-----------+----------+-----------------------------------------------
 id           | integer |           | not null | nextval('physical_document_id_seq'::regclass)
 title        | text    |           | not null | 
 md5_sum      | text    |           |          | 
 source_url   | text    |           |          | 
 content_type | text    |           |          | 
 cdn_object   | text    |           |          | 

Type of change

Please select the option(s) below that are most relevant:

• Bug fix
• New feature
• Breaking change

How Has This Been Tested?

Please describe the tests that you added to verify your changes.

Reviewer Checklist

• The PR represents a single feature (small driveby fixes are also ok)
• The PR includes tests that are sufficient for the level of risk
• The code is sufficiently commented, particularly in hard-to-understand areas
• Any required documentation updates have been made
• Any TODOs added are captured in future tickets
• No FIXMEs remain

[katybaulch]

Looks good to me. Config change may not be necessary, but doesn't affect the source code so nothing stopping merging.