Backport of docs: Add fault injection to Envoy extensions list into r…

…elease/1.18.x (#21100)

* backport of commit 891e357

* backport of commit 3a4bf18

---------

Co-authored-by: Blake Covarrubias <blake@covarrubi.as>

website/content/docs/connect/proxies/envoy-extensions/index.mdx

@@ -21,6 +21,7 @@ Instead of modifying Consul code, you can configure your services to use Envoy e
 Envoy extensions enable additional service mesh functionality in Consul by changing how the sidecar proxies behave. Extensions dynamically modify the configuration of Envoy proxies based on Consul configuration entries, enabling a wider set of use cases for the service mesh  traffic that passes through an Envoy proxy. Consul supports the following extensions:
 
 - External authorization
+- Fault injection
 - Lua
 - Lambda
 - OpenTelemetry Access Logging
@@ -31,6 +32,10 @@ Envoy extensions enable additional service mesh functionality in Consul by chang
 
 The `ext-authz` extension lets you configure external authorization filters for Envoy proxy so that you can route requests to external authorization systems. Refer to the [external authorization documentation](/consul/docs/connect/proxies/envoy-extensions/usage/ext-authz) for more information.
 
+### Fault injection
+
+The `fault-injection` extension lets you alter responses from an upstream service so that users can test the resilience of their system to different unexpected issues. Refer to the [fault injection documentation](/consul/docs/connect/manage-traffic/fault-injection) for more information.
+
 ### Lambda
 
 The `lambda` Envoy extension enables services to make requests to AWS Lambda functions through the mesh as if they are a normal part of the Consul catalog. Refer to the [Lambda extension documentation](/consul/docs/connect/proxies/envoy-extensions/usage/lambda) for more information.