RN-646: Add DataTable model to the database

[rohan-bes]

Issue RN-646:

Add the data_table table to the database.

fields:
id: id,
code: human readable unique identifier,
description: what the data table does
type: eg. (sql, google-sheets, transformation, etc.)
config: JSON for the specific data table config
permission_groups: Array of permission group names. Similar to how we do for permissions on data elements. A little conflicted about this, but honestly the permissions model for data tables still needs a bit of working out anyway, so this may just be a placeholder

[IgorNadj]

Happy to approve, but not sure if you want to just wait until you have a first implementation? I find that implementation details change things quite often. Up to you

[rohan-bes]

Happy to approve, but not sure if you want to just wait until you have a first implementation? I find that implementation details change things quite often. Up to you

@IgorNadj good point! Yeah I never know the best way to go with this kind of stuff 😅 I probably won't merge this one until I've got most of an initial implementation working on my local. But I like to break up the PRs rather than have one beastly one!