Keep track of OpCtxs created by PrimaryOnlyService threads and interrupt them at stepdown

Currently there is a small race condition where PrimaryOnlyService opCtxs can miss getting interrupted during stepdown. This can happen if a PrimaryOnlyService thread creates a new opCtx after the stepdown thread has already killed all OpCtxs as part of acquiring the RSTL lock, but before PrimaryOnlyService::onStepdown has been called.

Explicitly interrupting all OpCtxs owned by PrimaryOnlyServices in PrimaryOnlyService::onStepdown closes that window.