We need to update the architecture documentation to discuss the new approach to locking and queuing in the key-value layer.

AFAICT this new approach is enabled by the new concurrency control package/lock table referred to by this PR (and this one, and probably others).

Estimated scope of work:

• Update the architecture docs (probably the storage layer) to describe the new concurrency manager / how locking and queuing works

• Review other areas of the architecture docs to ensure they reference (or do not reference) this new layer, as appropriate