Adds info to the migration doc

Signed-off-by: Sagar Muchhal <muchhals@vmware.com>

docs/book/src/developer/providers/v1.2-to-v1.3.md

@@ -42,6 +42,7 @@ in Cluster API are kept in sync with the versions used by `sigs.k8s.io/controlle
 The default value is 0, meaning that the volume can be detached without any time limitations.
 - A new annotation `machine.cluster.x-k8s.io/exclude-wait-for-node-volume-detach` has been introduced that allows explicitly skip the waiting for node volume detaching.
 - The `Path` func in the `sigs.k8s.io/cluster-api/cmd/clusterctl/client/repository.Overrider` interface has been adjusted to also return an error.
+- Two new flags have been introduced to expose the configuration of the TLS Options for the webhook server, namely `--tls-min-version` and `--tls-cipher-suites`. Utility functions have been exposed under the `util/flags` package which can be used by the providers to implement the similar functionality.
 
 ### Other
 
@@ -66,3 +67,4 @@ The default value is 0, meaning that the volume can be detached without any time
   The variable `SkipUpgrade` could be set to revert to the old behaviour by making use of the `KUBERNETES_VERSION` variable and skipping the kubernetes upgrade.
 - cert-manager upgraded from v1.9.1 to v1.10.0.
 - Machine `providerID` is now being strictly checked for equality when compared against Kubernetes node `providerID` data. This is the expected criteria for correlating a Cluster API machine to its corresponding Kubernetes node, but historically this comparison was not strict, and instead compared only against the `ID` substring part of the full `providerID` string. Because different providers construct `providerID` strings differently, the `ID` substring is not uniformly defined and implemented across providers, and thus the existing `providerID` equality can not guarantee the correct Machine-Node correlation. It is very unlikely that this new behavior will break existing providers, but FYI: if strict `providerID` equality will degrade expected behaviors, you may need to update your provider implementation prior to adopting Cluster API v1.3.
+- The default minimum TLS version in use by the webhook servers is 1.2.