OSSMDOC-347: WASM Extensions support is always enabled

There's no need to explain how to enable it.

Also, while on it, made some changes to reflect the state of WASM
support in 2.1.

Author: jwendell

modules/ossm-extensions-wasm-deploy.adoc

@@ -10,7 +10,7 @@
 .Example ServiceMeshExtension resource extension.yaml
 [source,yaml]
 ----
-apiVersion: maistra.io/v1alpha1
+apiVersion: maistra.io/v1
 kind: ServiceMeshExtension
 metadata:
   name: header-append
@@ -19,8 +19,10 @@ spec:
   workloadSelector:
     labels:
       app: httpbin
-  config: test
-  image: quay.io/maistra-dev/header-append-filter:2.0
+  config:
+    first-header: some-value
+    another-header: another-value
+  image: quay.io/maistra-dev/header-append-filter:2.1
   phase: PostAuthZ
   priority: 100
 ----

modules/ossm-extensions-wasm-support.adoc

@@ -91,9 +91,7 @@ module: extension.wasm
 
 === Example Rust extension
 
-For a complete example that was built using the Rust SDK, take a look at the link:https://github.com/maistra/header-append-filter[header-append-filter]. The filter appends a header, called `custom-header`, to all responses, with the value depending on its configuration.
-
-include::modules/ossm-extensions-wasm-support.adoc[leveloffset=+2]
+For a complete example that was built using the Rust SDK, take a look at the link:https://github.com/maistra/header-append-filter[header-append-filter]. It is a simple filter that appends one or more headers to the HTTP responses, with their names and values taken out from the `config` field of the extension. See a sample configuration in the snippet below.
 
 include::modules/ossm-extensions-wasm-deploy.adoc[leveloffset=+2]
 
@@ -108,7 +106,7 @@ include::modules/ossm-extensions-wasm-deploy.adoc[leveloffset=+2]
 |The `spec.workloadSelector` field has the same semantic as the `spec.selector` field of the link:https://istio.io/v1.6/docs/reference/config/networking/gateway/#Gateway[Istio Gateway resource]. It will match a workload based on its Pod labels. If no `workloadSelector` is specified, the extension will be applied to all workloads in the namespace.
 
 |spec.config
-|This is a pass-through string field that is handed over to the extension. Syntax and semantics are dependent on the extension that you are deploying.
+|This is a structured field that will be handed over to the extension, with the semantics dependent on the extension you are deploying.
 
 |spec.image
 |A container image URI pointing to the image that holds the extension.