`FirstMessageTimestamp` enables members of the community to determine if
there are any messages they can fetch on the community channel(chat).
`FirstMessageTimestamp` is advertised by admin for each community chat
through `CommunityDescription`. It assumes admin is online frequently
enough to capture the first channel message.
For existing communities admin determines first message timestamp by
finding oldest chat message in its local database.
task: status-im/status-desktop#6731
We only write up migrations, down migrations are not always possible in sqlite or
too complex/too expensive. For example to remove a column you would have to duplicate
the table, copy over the data, delete and recreated.
This can be very expensive for some tables (user_messages for example), so should not be attempted.
Notes
One issue we faced multiple times is that updates to user_messages can be very
expensive, leading to slow upgrade times and interrupted migrations. So avoid
writes if not necessary.