remove personalisation from db

[terrazoon]

Description

We previously removed the recipient's phone number from the notifications table as part of trying to avoid our limitation of not having more than 10000 rows of data in notifications that contains PII. However, the phone number is present still in that table in another form -- encrypting inside the personalisation column, which contains everything in the csv row for that notification.

So the goal of this PR is to stop storing this personalisation info in the notifications table, and instead when we need personalisation info, we will fetch it from the ExpiringDict (our little cache) and if it is not present there, then we will fetch it from S3.

At this time we have not actually removed the phone_number and personalisation columns from the notifications table, we just no longer write to them. To remove these columns breaks many tests and requires many code changes and at the time this PR was made, there was another PR in progress (the "enums" PR) which was making similar, but conflicting changes everywhere.

Security Considerations

While not a security consideration per se, the goal of this PR is to move PII out of the database and rely on fetching it from S3.

[ccostino]

@terrazoon, could you please add a full description in here so that we can prep this PR for peer review? You can use the pull request template if you need a reference of what to include.

Once that information is in there, we can make sure it gets a peer review. 🙁 Thanks!

[A-Shumway42]

It looks great to me. I don't have major questions but if anyone takes a look and catches something I'm all for understanding.

[ccostino]

Thank you, @terrazoon!