Backport of Add documentation for proxy-config-map and xds_fetch_timeout_ms. into release/1.16.x (#19895)

backport of commit 85e942475a

Co-authored-by: Derek Menteer <derek.menteer@hashicorp.com>

website/content/docs/connect/proxies/envoy.mdx

@@ -357,6 +357,8 @@ defaults that are inherited by all services.
   - `exact_balance` - Inbound connections to the service use the
   [Envoy Exact Balance Strategy.](https://cloudnative.to/envoy/api-v3/config/listener/v3/listener.proto.html#config-listener-v3-listener-connectionbalanceconfig-exactbalance)
 
+- `xds_fetch_timeout_ms` - In milliseconds, the amount of time for Envoy to wait for EDS and RDS configuration before timing out. If not specified, this field uses Envoy's default value of `15000`, or 15 seconds. When an Envoy instance is configured with a large number of upstreams that take a significant amount of time to populate with data, setting this field to a higher value may prevent temporary disruption caused by unexpected timeouts.
+
 ### Proxy Upstream Config Options
 
 The following configuration items may be overridden directly in the

website/content/docs/k8s/annotations-and-labels.mdx

@@ -281,6 +281,11 @@ The following Kubernetes resource annotations could be used on a pod to control
   annotations:
     "consul.hashicorp.com/consul-sidecar-user-volume-mount": "[{\"name\": \"secrets-store-mount\", \"mountPath\": \"/mnt/secrets-store\"}]"
   ```
+- `consul.hashicorp.com/proxy-config-map` - JSON object specifying [Proxy Config Options](/consul/docs/connect/proxies/envoy#proxy-config-options). The proxy config map provides a low-level interface for setting configuration fields on a per-proxy basis during service registration. This configuration field is intended to be used in situations where a field does not exist in [service defaults configuration entries](/consul/docs/connect/config-entries/service-defaults) and another annotation does not provide explicit access to one of the Envoy configuration options.
+  ```yaml
+  annotations:
+    "consul.hashicorp.com/proxy-config-map": "{ \"xds_fetch_timeout_ms\": 30000 }"
+  ```
 
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