user-guide: reorg gateway-related doc pages

Signed-off-by: Fredi Raspall <fredi@githedgehog.com>

Author: Fredi-raspall

docs/user-guide/.pages

@@ -11,4 +11,8 @@ nav:
   - Observability:
     - o11y-config.md
     - grafana.md
+  - Gateway:
+    - gateway.md
+    - gateway-add.md
+    - gateway-failover.md
   - ...

docs/user-guide/gateway-add.md

@@ -1,4 +1,4 @@
-# Adding Gateway Node
+# Adding Gateways to the fabric
 
 This section covers adding a gateway node to an existing Fabric. Gateway nodes provide advanced network services (NAT, PAT, firewalling) by
 handling traffic between VPCs or between VPCs and externals using Gateway Peerings.

docs/user-guide/gateway.md

@@ -1,4 +1,4 @@
-# Gateway
+# Gateway overview
 
 The Gateway adds advanced network service capabilities to the fabric,
 complementing its fast, scalable connectivity. The fabric delivers efficient,

docs/user-guide/overview.md

@@ -8,6 +8,7 @@ This chapter gives an overview of the main features of Hedgehog Fabric and their
 - [**External Peering**](external.md): Details how to connect the fabric to external networks and services through border leaf peering.
 - [**Gateway**](gateway.md): Explains gateway configuration and gateway based Peerings for NAT and firewall functionality.
 - [**Adding a gateway to Fabric**](gateway-add.md): Explains how to add a gateway to a Fabric.
+- [**Gateway fail-over**](gateway-failover.md): Explains fail-over strategies when using multiple gateways.
 - [**Fabric Shrink/Expand**](shrink-expand.md): Guides users on adding, removing, or replacing switches within the fabric.
 - [**Switch Profiles and Port Naming**](profiles.md): Defines switch profiles, port naming conventions, and supported configurations.
 - [**Grafana Dashboards**](grafana.md): Provides insights into monitoring and visualization tools for tracking fabric performance and health.