Add support for bulk data loading that bypasses transaction logs

This feature will improve write bandwidth when initially loading data into a database. During the load, the range will not be readable. The design needs to consider how to get back to a consistent view of the world if a client dies during loading.

Proposed design:
* verify the range is empty, lock reads to the range, writes to the range that come from the tlogs are discarded
* disable data movement for the range
* directly send mutations to the server responsible for the range
* if one of the servers dies while loading mutations, clear the loaded data from the other servers and unlock the range
* unlocked the range
* re-enable data movement for the range

No files or tests are identified. Start by reviewing the proposed range-locking, transaction-log, direct-mutation, failure-recovery, and data-movement steps in the issue, then locate the corresponding implementation entry points; done would require a complete bulk-loading design with consistent recovery when a server dies.

Written by the indexing model from the issue text.