v0.44.0 release (#6611)

* cargo: update workspace crates version to v0.44.0

* news: v0.44.0 release notes

* graph: Disable postponed index creation

Pin postpone_attribute_index_creation to false regardless of the env
var, pending more testing in the hosted service. The runner-side
threshold path and the persistent once-only state remain in the codebase
but are unreachable until this is re-enabled.