server: update models to support semaphore groups

[sripwoud]

User should include a semaphore id commitment column.
So that we can automatically lookup users by email, and add their corresponding semaphore id to anonymous groups when a user decides to create an anonymous group that should be gated by email address ownership.

[jacque006]

I would recommend moving this to another table, as it could make it easier to add other ZK tech in the future as expanding the columns in the table, or making specific tables per identity scheme linked by User id (uid).

Something like:

Table: id_commitments
Columns:
uid foreign key to User, cascade delete if User deleted
commitment_id text unique , could be primary key

Would also make sense to add email there similar to yeap if we want users to be able to have multiple emails they can verify for different groups.