Automate `data_sources.last_approval_editor` logic to be automatically generated

[maxachis]

Context

• Currently, the last_approval_editor logic of data_sources is a string value which must be manually provided.
• This could be automated such that the last_approval_editor is determined automatically during the API call
• It may also be useful to convert this, in the database, to an integer foreign key linking last_approval_editor to the users.id column.

Requirements

• Determine the best approach to the above column.

Tests

• Tests would need modified (or created) if the above logic were to change.

Docs

• API documentation would be updated for various /data-sources endpoints, and possibly for other endpoints which pull data sources

Open questions

• See above

[josh-chamberlain]

@maxachis yes, fantastic catch. this is sort of a part of #32, because it's a field that is automatically updated by Airtable—but it need not be manual in v2.

[maxachis]

@josh-chamberlain With this, I want to get some clarification:

1. Do we expect anyone aside from admins to be able to modify these data sources?
2. Do we want to record solely who changed approval status, or who modified any value, or both separately?

[josh-chamberlain]

@maxachis

1. maybe eventually, but not right now
2. last_approval_editor should be only related to approval status. full edit history might happen in #477

[maxachis]

@josh-chamberlain For the moment, I intend to convert the existing last_approval_editor column to last_approval_editor_old for posterity. However, I can remove it entirely, as you desire.