Add docs section on regenerating expired CA certificates (#9709)

* Updated docs on regenerating built in CA

* review feedback

* Add sentence about expected behavior after update CA endpoint is used.

website/content/commands/tls/ca.mdx

@@ -40,3 +40,8 @@ Usage: `consul tls ca create [filename-prefix] [options]`
   will be added to the allowed DNS. If the UI is going to be served over HTTPS
   its DNS has to be added with `-additional-constraint`. It is not possible to
   add that after the fact! Defaults to false.
+
+- `cluster-id` - ClusterID of the consul cluster, requires `-domain` to be set as well.
+   When used this will cause URIs to be set with spiffeid.
+
+- `common-name` - Common Name of CA. Defaults to Consul Agent CA.

website/content/docs/connect/ca/index.mdx

@@ -211,3 +211,24 @@ servers.
 Currently both Consul and Vault CA providers _do_ support cross signing. As more
 providers are added this documentation will list any that this section applies
 to.
+
+### Recovering From Expired Certificates
+If the built-in CA provider is misconfigured or unavailable, Consul service mesh requests eventually
+stop functioning due to expiration of intermediate and root certificates. To recover manually, use the
+[CLI helper](/commands/tls/ca#consul-tls-ca-create) to generate CA certificates.
+
+
+#### Example - Regenerating the built in CA
+```shell-session
+$ consul tls ca create -cluster-id test -common-name "Consul Agent CA" -days=365 -domain consul
+  ==> Saved consul-agent-ca.pem
+  ==> Saved consul-agent-ca-key.pem
+```
+The example above generates a new CA with a validity of 365 days. The cluster-id argument is specific
+to each cluster and can be looked up by examining the `TrustDomain` field in
+the [List CA Roots](/api-docs/connect/ca#list-ca-root-certificates) endpoint.
+
+The contents of the generated cert and private key files from the above step should then be used with
+the [Update CA Configuration](/api/connect/ca#update-ca-configuration) endpoint. Once the CA configuration is
+updated on the primary datacenter, all secondary datacenters will pick up the changes and regenerate their intermediate
+and leaf certificates, after which any new requests that require certificate verification will succeed.