add references to the "Deploy Istio egress gateway" to the sections that use it (#3535)

content/blog/2018/egress-mongo/index.md

@@ -233,6 +233,8 @@ In this section you handle the case when you need to direct the traffic through
 connections from the MongoDB client to the egress gateway, by matching the IP of the MongoDB host (a CIDR block of
   length 32). The egress gateway forwards the traffic to the MongoDB host, by its hostname.
 
+1.  [Deploy Istio egress gateway](/docs/examples/advanced-gateways/egress-gateway/#deploy-istio-egress-gateway).
+
 1.  Create a `ServiceEntry` for the MongoDB service, this time with `resolution` `DNS`. Specifying the resolution as
     `DNS` instructs the egress gateway to perform a DNS query to get the IP address of the MongoDB host. Note that the
     IP of the MongoDB host used by the MongoDB client (the `ratings` service) is not known to the egress gateway.
@@ -556,6 +558,8 @@ The egress gateway forwards the traffic to the MongoDB host. Note that the sidec
 to be 443. The egress gateway accepts the MongoDB traffic on the port 443, matches the MongoDB host by SNI, and rewrites
  the port again to be the port of the MongoDB server.
 
+1.  [Deploy Istio egress gateway](/docs/examples/advanced-gateways/egress-gateway/#deploy-istio-egress-gateway).
+
 1.  Create a `ServiceEntry` for the MongoDB service:
 
     {{< text bash >}}

content/docs/examples/advanced-gateways/egress-gateway-tls-origination/index.md

@@ -40,6 +40,8 @@ TLS origination for traffic to external services.
     $ export SOURCE_POD=$(kubectl get pod -l app=sleep -o jsonpath={.items..metadata.name})
     {{< /text >}}
 
+*   [Deploy Istio egress gateway](/docs/examples/advanced-gateways/egress-gateway/#deploy-istio-egress-gateway).
+
 ## Perform TLS origination with an egress gateway
 
 This section describes how to perform the same TLS origination as in the

content/docs/examples/advanced-gateways/egress_sni_monitoring_and_policies/index.md

@@ -11,6 +11,8 @@ example extends that example to show how to configure SNI monitoring and apply p
 
 {{< boilerplate before-you-begin-egress >}}
 
+*   [Deploy Istio egress gateway](/docs/examples/advanced-gateways/egress-gateway/#deploy-istio-egress-gateway).
+
 *  Configure traffic to `*.wikipedia.org` by following
    [the steps](/docs/examples/advanced-gateways/wildcard-egress-hosts#wildcard-configuration-for-arbitrary-domains) in
    [Configure Egress Traffic using Wildcard Hosts](/docs/examples/advanced-gateways/wildcard-egress-hosts/) example,

content/docs/examples/advanced-gateways/wildcard-egress-hosts/index.md

@@ -21,6 +21,8 @@ without the need to specify every language's site separately.
 
 {{< boilerplate before-you-begin-egress >}}
 
+*   [Deploy Istio egress gateway](/docs/examples/advanced-gateways/egress-gateway/#deploy-istio-egress-gateway).
+
 ## Configure direct traffic to a wildcard host
 
 The first, and simplest, way to access a set of hosts within a common domain is by configuring