Updates docs with new support for primary cookie name in istio router

Signed-off-by: Renato Vassão <renato.vassao@mindbodyonline.com>

Author: renatovassaomb

docs/gitbook/tutorials/istio-progressive-delivery.md

@@ -404,6 +404,9 @@ You can load `app.example.com` in your browser and refresh it until you see the
 All subsequent requests after that will be served by `podinfo:6.0.1` and not `podinfo:6.0.0` because of the session affinity
 configured by Flagger with Istio.
 
+To configure stickiness for the Primary deployment to ensure fair weighted traffic routing, please
+checkout the [deployment strategies docs](../usage/deployment-strategies.md#canary-release-with-session-affinity).
+
 ## Traffic mirroring
 
 ![Flagger Canary Traffic Shadowing](https://raw.githubusercontent.com/fluxcd/flagger/main/docs/diagrams/flagger-canary-traffic-mirroring.png)

docs/gitbook/usage/deployment-strategies.md

@@ -474,7 +474,7 @@ can also configure stickiness for the Primary deployment. You can configure this
       primaryCookieName: primary-flagger-cookie
 ```
 
-> Note: This is only supported for the Gateway API provider for now.
+> Note: This is only supported for the Gateway API and Istio providers for now.
 
 Let's understand what the above configuration does. All the session affinity stuff in the above section
 still occurs, but now the response header for requests routed to the primary deployment also include a