Follow+Notes: Add grant followers table to database

[TylerHendrickson]

Subtask of [STORY]: Update 'Status' to 'Follow + Note' feature #2960

Blocked by

N/A

Blocks

• (Library)

Definition of Done

A new Knex migration is added that creates the table needed for storing followers of grants.

Implementation Details

This requires the following new tables to be created:

• Table grant_followers
  • Columns:
    • id: serial, not null, primary key
    • grant_id: text, not null, foreign key to grants.grant_id
    • user_id: int, not null, foreign key to users.id
    • created_at: timestamp with time zone, not null, default now()
  • Unique index idx_grant_id_user_id on columns (grant_id, user_id)

[TylerHendrickson]

This issue is small enough that it should be merged with #3203