Allow seeding databases with content from existing group databases

[athoscouto]

Adds the --from-db flag to the turso db create command.

Example:

turso db create new-db --from-db base-db

This will create a new database called new-db with schema and data copied from base-db.

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Caveats:

• It will only work if base-db is a group database.

$ turso db create new-db --from-db non-group-db
Error: could not create database new-db: forked database 'non-group-db' must belong to a group

• It works with the --group $GROUP flag, but base-db must be inside $GROUP.

> turso db create new-db --from-db base-db --group group2
Error: could not create database new-db: can only fork databases within the same group: database base-db is not part of group group2