API and scenario tests for PROMETHEUS listeners.

This patch adds API and scenario tests for PROMETHEUS listeners. This
includes scenario tests that connect to the metrics endpoint.

Depends-On: https://review.opendev.org/c/openstack/octavia/+/812258
Change-Id: Ia46d8c0967bc5b0f7cd11b6e3ca3a4e03c0bc138
diff --git a/octavia_tempest_plugin/config.py b/octavia_tempest_plugin/config.py
index 4d1543b..502bdec 100644
--- a/octavia_tempest_plugin/config.py
+++ b/octavia_tempest_plugin/config.py
@@ -285,6 +285,8 @@
                 help="Whether the log offload tests will run. These require "
                      "the tempest instance have access to the log files "
                      "specified in the tempest configuration."),
+    cfg.BoolOpt('prometheus_listener_enabled', default=True,
+                help="Whether the PROMETHEUS listener tests will run."),
 ]
 
 # Extending this enforce_scope group defined in tempest