[lib] Rename failuresAfterPolicyAcknowledgment to initFailureCountAfterPolicyAcknowledgment

Summary:
I think it's good to clarify what kind of failure it is (an initialization failure).

Depends on D12367

Test Plan: Flow

Reviewers: tomek

Reviewed By: tomek

Differential Revision: https://phab.comm.dev/D12368