docs: add multi-host connection string info to postgres secrets API docs (#16780)

* Add multihost connection string information to postgres API docs

* Add note about replication manager

website/content/docs/secrets/databases/postgresql.mdx

@@ -32,7 +32,7 @@ options, including SSL options, can be found in the [pgx][pgxlib] and
 
 1.  Enable the database secrets engine if it is not already enabled:
 
-    ```text
+    ```shell-session
     $ vault secrets enable database
     Success! Enabled the database secrets engine at: database/
     ```
@@ -42,9 +42,9 @@ options, including SSL options, can be found in the [pgx][pgxlib] and
 
 1.  Configure Vault with the proper plugin and connection information:
 
-    ```text
+    ```shell-session
     $ vault write database/config/my-postgresql-database \
-        plugin_name=postgresql-database-plugin \
+        plugin_name="postgresql-database-plugin" \
         allowed_roles="my-role" \
         connection_url="postgresql://{{username}}:{{password}}@localhost:5432/" \
         username="vaultuser" \
@@ -54,9 +54,9 @@ options, including SSL options, can be found in the [pgx][pgxlib] and
 1.  Configure a role that maps a name in Vault to an SQL statement to execute to
     create the database credential:
 
-    ```text
+    ```shell-session
     $ vault write database/roles/my-role \
-        db_name=my-postgresql-database \
+        db_name="my-postgresql-database" \
         creation_statements="CREATE ROLE \"{{name}}\" WITH LOGIN PASSWORD '{{password}}' VALID UNTIL '{{expiration}}'; \
             GRANT SELECT ON ALL TABLES IN SCHEMA public TO \"{{name}}\";" \
         default_ttl="1h" \
@@ -72,7 +72,7 @@ the proper permission, it can generate credentials.
 1.  Generate a new credential by reading from the `/creds` endpoint with the name
     of the role:
 
-    ```text
+    ```shell-session
     $ vault read database/creds/my-role
     Key                Value
     ---                -----