[web/native] Migrate keyserverStore to new tables

Summary:
Migrates the current data in one keyserver table to two. It works a bit unusually but the general gist is:

• Copy the data from keyservers to keyserver_synced_data
• Fetch the data in the migrations (db ops will merge the data from keyserver and keyserver_synced_data and so return the correct KeyserverInfo)
• Save the data in the migration (db ops will now split the data correctly into two tables)

Also adds the non-synced keyservers table to backup blocklist.

Depends on https://phab.comm.dev/D11481

Test Plan: Make sure the migration runs correctly on both web and native. Compare the results from before the migration and after -> the keyserver infos should be the same (but urlPrefix is in a different table).

Reviewers: kamil, marcin

Reviewed By: kamil, marcin

Subscribers: ashoat, tomek

Differential Revision: https://phab.comm.dev/D11482