[keyserver] Add a thread column to invite links
Summary:
This column is used to support links to chats
Test Plan:
Run the migration and check if the column was added. Create an empty DB and check if the column was created.
Also, checked if the index was created in both cases.
Reviewers: inka, ginsu
Reviewed By: ginsu
Subscribers: ashoat
Differential Revision: https://phab.comm.dev/D12351