Add Windows as unsupported for Egress gateway and sync the strucuture for AWS, Azure and On premise (tigera#2453)

Author: sujeet-kr

calico-enterprise/networking/egress/egress-gateway-aws.mdx

@@ -178,6 +178,7 @@ an instance (for example when scaling up the cluster).
 **Not Supported**
 
 - Amazon VPC CNI
+- Windows
 
   $[prodname] CNI and IPAM is required. The ability to control the egress gateway’s IP is a feature of $[prodname] CNI and IPAM. AWS VPC CNI does not support that feature, so it is incompatible with egress gateways.
 

calico-enterprise/networking/egress/egress-gateway-azure.mdx

@@ -88,6 +88,7 @@ VNet peering, or to external datacenters through ExpressRoute, allowing communic
 **Not Supported**
 
 - Azure VNet CNI
+- Windows
 
 $[prodname] CNI and IPAM are required. The ability to control the egress gateway’s IP is a feature of $[prodname] CNI and IPAM. Azure VNet CNI does not support that feature, so it is incompatible with egress gateways.
 

calico-enterprise/networking/egress/egress-gateway-on-prem.mdx

@@ -154,15 +154,16 @@ patch release.
 
 ## Before you begin
 
-**Unsupported**
-
-- GKE
-
 **Required**
 
 - Calico CNI
 - Open port UDP 4790 on the host
 
+**Not supported**
+
+- GKE
+- Windows
+
 ## How to
 
 - [Enable egress gateway support](#enable-egress-gateway-support)