Fix indentation for secretRef in authentication docs (#1135)

Author: avinashupadhya99

modules/manage/partials/authentication.adoc

@@ -753,7 +753,7 @@ spec:
     auth:
       sasl:
         enabled: true
-      secretRef: redpanda-superusers
+        secretRef: redpanda-superusers
     config:
       cluster:
         sasl_mechanisms:
@@ -779,7 +779,7 @@ Helm::
 auth:
   sasl:
     enabled: true
-  secretRef: redpanda-superusers
+    secretRef: redpanda-superusers
 config:
   cluster:
     sasl_mechanisms:
@@ -942,7 +942,7 @@ spec:
     auth:
       sasl:
         enabled: true
-      secretRef: redpanda-superusers
+        secretRef: redpanda-superusers
     config:
       cluster:
         sasl_mechanisms:
@@ -974,7 +974,7 @@ Helm::
 auth:
   sasl:
     enabled: true
-  secretRef: redpanda-superusers
+    secretRef: redpanda-superusers
 config:
   cluster:
     sasl_mechanisms:
@@ -1393,7 +1393,7 @@ spec:
     auth:
       sasl:
         enabled: true
-      secretRef: redpanda-superusers
+        secretRef: redpanda-superusers
     config:
       cluster:
         admin_api_require_auth: true