Fixes openshift#52922: Add documentation for HAProxy option persist

Author: Thomas Wöckinger

modules/nw-route-specific-annotations.adoc

@@ -42,6 +42,7 @@ Note: Using this annotation provides basic protection against distributed denial
 | Sets a whitelist for the route. The whitelist is a space-separated list of IP addresses and CIDR ranges for the approved source addresses. Requests from IP addresses that are not in the whitelist are dropped.
 
 The maximum number of IP addresses and CIDR ranges allowed in a whitelist is 61.|
+|`haproxy.router.openshift.io/persist` | When an HTTP request reaches a backend with a cookie which references a dead server, by default it is redispatched to another server. It is possible to force the request to be sent to the dead server first using "option persist". A common use case is when servers are under extreme load and spend their time flapping. In this case, the users would still be directed to the server they opened the session on, in the hope they would be correctly served. | 
 |`haproxy.router.openshift.io/hsts_header` | Sets a Strict-Transport-Security header for the edge terminated or re-encrypt route. |
 |`haproxy.router.openshift.io/log-send-hostname` | Sets the `hostname` field in the Syslog header. Uses the hostname of the system. `log-send-hostname` is enabled by default if any Ingress API logging method, such as sidecar or Syslog facility, is enabled for the router. |
 |`haproxy.router.openshift.io/rewrite-target` | Sets the rewrite path of the request on the backend. |