fix(doc): update secretManager distributed configuration documentation (micronaut-projects#1920)

Author: charlesjourdain

src/main/docs/guide/distributedconfiguration/distributedconfigurationsecretsmanager.adoc

@@ -30,12 +30,13 @@ micronaut:
   config-client:
     enabled: true
 aws:
-  secretsmanager:
-    secrets:
-      - secret-name: rds
-        prefix: datasources.default
-      - secret-name: rds_backup
-        prefix: datasources.backup
+  client:
+    secretsmanager:
+      secrets:
+        - secret-name: rds
+          prefix: datasources.default
+        - secret-name: rds_backup
+          prefix: datasources.backup
 ----
 
 Note that `secret-name` is a name suffix of the secret configured in AWS Secret Manager. For example, to add `rds_backup` configuration for a `production` environment, add the `rds_backup` configuration entry to the `src/main/resources/bootstrap.yml` as shown in the example above. Also, create RDS secret in AWS Secret Manager with name `/config/application_prod/rds_backup` or `/config/[APPLICATION_NAME]_prod/rds_backup`.