#10121 points out that we're using md5 functions still. This PR updates
our migrations to no longer use md5 at all (so if you haven't run the
migrations, you won't get email hashes until you get to the included
migration with this PR). If you've already run the migrations, we'll
drop the existing `email_hash varchar(32)` column and replace it with a
`email_hash TEXT` column.
We're also replacing the md5 function with `encode(sha256(email),
'hex')`. encode has been supported since PG10, sha256 came with PG11.
Do we want an index on the email_hash? I wasn't sure, but if we want to
do lookup we probably should have an index on it (though not a unique
one)
Adding email_hash column to users table.
We will update all existing users to have hashed email.
All new users will also get the hash.
We are fine to use md5, because we just need uniqueness. We have emails
in events table stored anyways, so it is not sensitive.
