roles/haproxy: Basic setup for HAproxy

The *haproxy* installs HAproxy and sets up basic configuration for it.
It configures the systemd unit to launch the service with the `-f
/etc/haproxy` arguments, which will cause it to load all files from the
`/etc/haproxy` directory, instead of just `/etc/haproxy/haproxy.cfg`.
This will allow other roles to add frontend and backend configuration by
adding additional files to this directory.

roles/haproxy/templates/global.cfg.j2

@@ -0,0 +1,18 @@
+#---------------------------------------------------------------------
+# Global settings
+#---------------------------------------------------------------------
+global
+    log         /dev/log local0
+
+    pidfile     /var/run/haproxy.pid
+    maxconn     4000
+    user        haproxy
+    group       haproxy
+    daemon
+
+    # turn on stats unix socket
+    stats socket /var/lib/haproxy/stats
+
+    # utilize system-wide crypto-policies
+    ssl-default-bind-ciphers PROFILE=SYSTEM
+    ssl-default-server-ciphers PROFILE=SYSTEM