Retry for ProvisioningRequests KEP (kubernetes-sigs#1355)

* Retry for ProvisioningRequests KEP

* review comments

* Added a note about defaults for retry mechanism

keps/1136-provisioning-request-support/README.md

@@ -105,6 +105,13 @@ If the `ProvisioningRequest` fails, fail the `AdmissionCheck`.
 the provisioning request should also be deleted (the last one can be achieved via
 OwnerReference).
 
+* Retry ProvisioningRequests with respect to the `RetryConfig` configuration in
+the `ProvisioningRequestConfig`. For each attempt a new provisioning request is
+created with the suffix indicating the attempt number. The corresponding admission
+check will remain in the `Pending` state until the retries end. The max number
+of retries is 3, and the interval between attempts grows exponentially, starting
+from 1min (1, 2, 4 min).
+
 The definition of `ProvisioningRequestConfig` is relatively simple and is based on
 what can be set in `ProvisioningRequest`.