Beef up AR migrations with null:false

[ConnorSheremeta]

#1685 from #1272 (comment) Beefed up AR migrations by stating that certain attributes cannot be null

Also in PR #1704

[murny]

So we might have to be careful here editing existing migrations like this (i assume we are probably okay here, as these haven't been ran in production yet). So if we all good, then this looks good 👍 (otherwise we will have to add seperate migrations for adding these as null: false)

We may want to add a ticket in the backlog to make sure we have the same validations on the model layer for this too? Or we could tackle it in this PR, but whatever we decide as long as its getting done. (Some have it already like communities, but collections for example doesn't have a validation for title being required on model level)

Also we should probably run these so the schema.rb file gets updated with these new changes

[ConnorSheremeta]

I've added a constraint on the model, the only one that was missing was the collection title as far as I can tell. I have the schema changes in #1704 but I didn't add them here, I thought it would cause problems... I can definitely run through the migration process and commit the new schema db file here if there aren't any issues in doing so. My knowledge of migrations and impact on the schema file doesn't run too deep. I believe there are other changes to the schema that occur during the migrations and rake task that aren't in integration_postmigration that I could add as well, this might be better off in another PR.

[ConnorSheremeta]

It has been decided to not commit the changes to schema.db here