chore: Add docs for ssh tunneling

RESOURCES/FEATURE_FLAGS.md

@@ -61,6 +61,7 @@ These features are **finished** but currently being tested. They are usable, but
 - GENERIC_CHART_AXES
 - GLOBAL_ASYNC_QUERIES [(docs)](https://github.com/apache/superset/blob/master/CONTRIBUTING.md#async-chart-queries)
 - RLS_IN_SQLLAB
+- SSH_TUNNELING [(docs)](https://superset.apache.org/docs/installation/setup-ssh-tunneling)
 - USE_ANALAGOUS_COLORS
 - UX_BETA
 - VERSIONED_EXPORT

docs/docs/installation/setup-ssh-tunneling.mdx

@@ -0,0 +1,21 @@
+---
+title: Setup SSH Tunneling
+hide_title: true
+sidebar_position: 13
+version: 1
+---
+
+## SSH Tunneling
+
+1. Turn on feature flag
+    - Change [`SSH_TUNNELING`](https://github.com/apache/superset/blob/eb8386e3f0647df6d1bbde8b42073850796cc16f/superset/config.py#L489) to `True`
+    - If you want to add more security when establishing the tunnel we allow users to overwrite the `SSHTunnelManager` class (here)[https://github.com/apache/superset/blob/eb8386e3f0647df6d1bbde8b42073850796cc16f/superset/config.py#L507]
+    - You can also set the [`SSH_TUNNEL_LOCAL_BIND_ADDRESS`](https://github.com/apache/superset/blob/eb8386e3f0647df6d1bbde8b42073850796cc16f/superset/config.py#L508) this the host address where the tunnel will be accessible on your VPC
+
+2. Create database w/ ssh tunnel enabled
+    - With the feature flag enabled you should now see ssh tunnel toggle.
+    - Click the toggle to enables ssh tunneling and add your credentials accordingly.
+        - Superset allows for 2 different type authenticaion (Basic + Private Key). These credentials should come from your service provider.
+
+3. Verify data is flowing
+    - Once SSH tunneling has been enabled, go to SQL Lab and write a query to verify data is properly flowing.