Add guide for UpstreamSettingsPolicy (#2987)

Problem: As a user, I want an example of how to configure upstream 
settings for my application.

Solution: Add a how-to guide describing how to configure 
upstream zone size and keepalives for services. Also adds 
UpstreamSettingsPolicy to the table in the custom policies 
document and moves the custom policies document closer 
to the top of the overview page to increase visibility.

Author: kate-osborn

examples/upstream-settings-policy/1m-zone-size.yaml

@@ -0,0 +1,13 @@
+apiVersion: gateway.nginx.org/v1alpha1
+kind: UpstreamSettingsPolicy
+metadata:
+  name: 1m-zone-size
+spec:
+  targetRefs:
+    - group: core
+      kind: Service
+      name: tea
+    - group: core
+      kind: Service
+      name: coffee
+  zoneSize: 1m

examples/upstream-settings-policy/README.md

@@ -1,4 +1,3 @@
 # UpstreamSettingsPolicy
 
-This directory contains example YAMLs for testing the UpstreamSettingsPolicy CRD. Eventually, this will be converted
-into a how-to-guide.
+This directory contains the YAML files used in the [UpstreamSettingsPolicy](https://docs.nginx.com/nginx-gateway-fabric/how-to/traffic-management/upstream-settings/) guide.

examples/upstream-settings-policy/cafe.yaml renamed to examples/upstream-settings-policy/app.yaml

@@ -11,7 +11,7 @@ spec:
   rules:
   - matches:
     - path:
-        type: PathPrefix
+        type: Exact
         value: /coffee
     backendRefs:
     - name: coffee

examples/upstream-settings-policy/cafe-routes.yaml renamed to examples/upstream-settings-policy/httproutes.yaml

@@ -1,15 +1,11 @@
 apiVersion: gateway.nginx.org/v1alpha1
 kind: UpstreamSettingsPolicy
 metadata:
-  name: upstream-settings-policy
+  name: upstream-keepalives
 spec:
-  zoneSize: 512k
   targetRefs:
     - group: core
       kind: Service
       name: coffee
   keepAlive:
     connections: 32
-    requests: 1001
-    time: 300s
-    timeout: 60s

examples/upstream-settings-policy/upstream-settings-policy.yaml renamed to examples/upstream-settings-policy/upstream-keepalives.yaml

@@ -64,7 +64,7 @@ To enable tracing, you must configure two resources:
 
   The `NginxProxy` resource contains configuration for the collector, and applies to all Gateways and routes under the GatewayClass. It does not enable tracing, but is a prerequisite to the next piece of configuration.
 
-- `ObservabilityPolicy`: This resource is a [Direct PolicyAttachment](https://gateway-api.sigs.k8s.io/reference/policy-attachment/) that targets HTTPRoutes or GRPCRoutes. It is created by the [application developer](https://gateway-api.sigs.k8s.io/concepts/roles-and-personas/) and enables tracing for a specific route or routes. It requires the `NginxProxy` resource to exist in order to complete the tracing configuration.
+- `ObservabilityPolicy`: This resource is a [Direct Policy Attachment](https://gateway-api.sigs.k8s.io/reference/policy-attachment/) that targets HTTPRoutes or GRPCRoutes. It is created by the [application developer](https://gateway-api.sigs.k8s.io/concepts/roles-and-personas/) and enables tracing for a specific route or routes. It requires the `NginxProxy` resource to exist in order to complete the tracing configuration.
 
 For all the possible configuration options for these resources, see the [API reference]({{< relref "reference/api.md" >}}).
 

site/content/how-to/monitoring/tracing.md

@@ -19,7 +19,7 @@ The settings in `ClientSettingsPolicy` correspond to the following NGINX directi
 - [`keepalive_time`](<https://nginx.org/en/docs/http/ngx_http_core_module.html#keepalive_time>)
 - [`keepalive_timeout`](<https://nginx.org/en/docs/http/ngx_http_core_module.html#keepalive_timeout>)
 
-`ClientSettingsPolicy` is an [Inherited PolicyAttachment](https://gateway-api.sigs.k8s.io/reference/policy-attachment/) that can be applied to a Gateway, HTTPRoute, or GRPCRoute in the same namespace as the `ClientSettingsPolicy`.
+`ClientSettingsPolicy` is an [Inherited Policy Attachment](https://gateway-api.sigs.k8s.io/reference/policy-attachment/) that can be applied to a Gateway, HTTPRoute, or GRPCRoute in the same namespace as the `ClientSettingsPolicy`.
 
 When applied to a Gateway, the settings specified in the `ClientSettingsPolicy` affect all HTTPRoutes and GRPCRoutes attached to the Gateway. This allows Cluster Operators to set defaults for all applications using the Gateway.