haproxy-config.template: Fix power-of-two balancing

Update the set of allowed balancing algorithms to include "random", i.e.,
the "Power of Two Random Choices" algorithm.  An earlier commit was
supposed to make "random" the default algorithm but failed to add it to the
set of allowed algorithms.  As a result, the template would configure
HAProxy to the "roundrobin" algorithm by default.  This commit makes it so
the effective default is "random", as intended in the earlier commit.

Follow-up to commit dbc994c.

This commit fixes bug 1988801.

https://bugzilla.redhat.com/show_bug.cgi?id=1988801

* images/router/haproxy/conf/haproxy-config.template: Fix
$balanceAlgoPattern to match "random".

images/router/haproxy/conf/haproxy-config.template

@@ -19,7 +19,7 @@
 {{- $cookieNamePattern := `[a-zA-Z0-9_-]+` -}}
 
 {{- /* balanceAlgoPattern matches valid options for the haproxy.router.openshift.io/balance annotation. */}}
-{{- $balanceAlgoPattern := "roundrobin|leastconn|source" -}}
+{{- $balanceAlgoPattern := "roundrobin|leastconn|source|random" -}}
 
 {{- $timeSpecPattern := `[1-9][0-9]*(us|ms|s|m|h|d)?` }}