Add SnippetsFilter guide (#2721)

Add SnippetsFilters guide.

Problem: We want a guide for using SnippetsFilters.

Solution: Add a SnippetsFilters guide.

Testing: Verified using make watch Hugo command.

examples/snippets-filter/README.md

@@ -1,3 +1,3 @@
 # SnippetsFilter
 
-This directory contains example YAMLs for testing SnippetsFilter. Eventually, this will be converted into a how-to guide.
+This directory contains the YAML files used in the [SnippetsFilter API](https://docs.nginx.com/nginx-gateway-fabric/how-to/traffic-management/snippets/) guide.

examples/snippets-filter/app.yaml

@@ -0,0 +1,65 @@
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: coffee
+spec:
+  replicas: 1
+  selector:
+    matchLabels:
+      app: coffee
+  template:
+    metadata:
+      labels:
+        app: coffee
+    spec:
+      containers:
+        - name: coffee
+          image: nginxdemos/nginx-hello:plain-text
+          ports:
+            - containerPort: 8080
+---
+apiVersion: v1
+kind: Service
+metadata:
+  name: coffee
+spec:
+  ports:
+    - port: 80
+      targetPort: 8080
+      protocol: TCP
+      name: http
+  selector:
+    app: coffee
+---
+apiVersion: apps/v1
+kind: Deployment
+metadata:
+  name: tea
+spec:
+  replicas: 1
+  selector:
+    matchLabels:
+      app: tea
+  template:
+    metadata:
+      labels:
+        app: tea
+    spec:
+      containers:
+        - name: tea
+          image: nginxdemos/nginx-hello:plain-text
+          ports:
+            - containerPort: 8080
+---
+apiVersion: v1
+kind: Service
+metadata:
+  name: tea
+spec:
+  ports:
+    - port: 80
+      targetPort: 8080
+      protocol: TCP
+      name: http
+  selector:
+    app: tea

examples/snippets-filter/gateway.yaml

@@ -0,0 +1,11 @@
+apiVersion: gateway.networking.k8s.io/v1
+kind: Gateway
+metadata:
+  name: gateway
+spec:
+  gatewayClassName: nginx
+  listeners:
+    - name: http
+      port: 80
+      protocol: HTTP
+      hostname: "*.example.com"

examples/snippets-filter/httproutes.yaml

@@ -0,0 +1,37 @@
+apiVersion: gateway.networking.k8s.io/v1
+kind: HTTPRoute
+metadata:
+  name: coffee
+spec:
+  parentRefs:
+    - name: gateway
+      sectionName: http
+  hostnames:
+    - "cafe.example.com"
+  rules:
+    - matches:
+        - path:
+            type: PathPrefix
+            value: /coffee
+      backendRefs:
+        - name: coffee
+          port: 80
+---
+apiVersion: gateway.networking.k8s.io/v1
+kind: HTTPRoute
+metadata:
+  name: tea
+spec:
+  parentRefs:
+    - name: gateway
+      sectionName: http
+  hostnames:
+    - "cafe.example.com"
+  rules:
+    - matches:
+        - path:
+            type: PathPrefix
+            value: /tea
+      backendRefs:
+        - name: tea
+          port: 80

examples/snippets-filter/no-delay-rate-limiting-sf.yaml

@@ -0,0 +1,10 @@
+apiVersion: gateway.nginx.org/v1alpha1
+kind: SnippetsFilter
+metadata:
+  name: no-delay-rate-limiting-sf
+spec:
+  snippets:
+    - context: http
+      value: limit_req_zone $binary_remote_addr zone=no-delay-rate-limiting-sf:10m rate=1r/s;
+    - context: http.server.location
+      value: limit_req zone=no-delay-rate-limiting-sf burst=3 nodelay;

examples/snippets-filter/rate-limiting-sf.yaml

@@ -0,0 +1,10 @@
+apiVersion: gateway.nginx.org/v1alpha1
+kind: SnippetsFilter
+metadata:
+  name: rate-limiting-sf
+spec:
+  snippets:
+    - context: http
+      value: limit_req_zone $binary_remote_addr zone=rate-limiting-sf:10m rate=1r/s;
+    - context: http.server.location
+      value: limit_req zone=rate-limiting-sf burst=3;