Currently the TenantMigrationDonorAccessBlocker requires passing in a recipientConnectionString to its constructor. In shard split this becomes difficult because we need to consult the local replset config in order to build that connection string each time it's required. It's impossible to do that on recovery, since the access blocker recovery code is run before a local config is installed. This ticket will cover making this field optional, since it's only used to generate a debug string.

This is a stop-gap fix until we implement SERVER-64618, which will be a more comprehensive fix for shard split access blocking.