Prev. we inserted data for tracking issued names into the `issuedNames` table
during `sa.AddCertificate`. A more robust solution is to do this during
`sa.AddPrecertificate` since this is when we've truly committed to having
issued for the names.
The new SA `WriteIssuedNamesPrecert` feature flag enables writing this table
during `AddPrecertificate`. The legacy behaviour continues with the flag
enabled or disabled but is updated to tolerate duplicate INSERT errors so that
it is possible to deploy this change across multiple SA instances safely.
Along the way I also updated `SA.AddPrecertificate` to perform its two
`INSERT`s in a transaction using the `db.WithTransaction` wrapper.
Resolves https://github.com/letsencrypt/boulder/issues/4565
608c381444