Move Using Secrets to h2. for top of page linking (#14041)

This seems like one of the key sections of the page users are likely to want to come directly to and matches the setup of some existing pages such as https://kubernetes.io/docs/concepts/workloads/controllers/jobs-run-to-completion/#advanced-usage

content/en/docs/concepts/configuration/secret.md

@@ -359,7 +359,7 @@ echo 'MWYyZDFlMmU2N2Rm' | base64 --decode
 1f2d1e2e67df
 ```
 
-### Using Secrets
+## Using Secrets
 
 Secrets can be mounted as data volumes or be exposed as
 {{< glossary_tooltip text="environment variables" term_id="container-env-variables" >}}
@@ -368,7 +368,7 @@ system, without being directly exposed to the pod.  For example, they can hold
 credentials that other parts of the system should use to interact with external
 systems on your behalf.
 
-#### Using Secrets as Files from a Pod
+### Using Secrets as Files from a Pod
 
 To consume a Secret in a volume in a Pod:
 
@@ -560,7 +560,7 @@ A container using a Secret as a
 Secret updates.
 {{< /note >}}
 
-#### Using Secrets as Environment Variables
+### Using Secrets as Environment Variables
 
 To use a secret in an {{< glossary_tooltip text="environment variable" term_id="container-env-variables" >}}
 in a pod:
@@ -613,7 +613,7 @@ echo $SECRET_PASSWORD
 1f2d1e2e67df
 ```
 
-#### Using imagePullSecrets
+### Using imagePullSecrets
 
 An imagePullSecret is a way to pass a secret that contains a Docker (or other) image registry
 password to the Kubelet so it can pull a private image on behalf of your Pod.