Add conf option for listener connection limit

The patch provides configuration option to define listener connection
limit to make chance to adjust connections for environments with various
amount of resources.

Related-PRODX: PRODX-19517
Change-Id: I435a0a38440860b3d8022aa164f6288aced1d70a
diff --git a/octavia_tempest_plugin/config.py b/octavia_tempest_plugin/config.py
index 4d1543b..929a912 100644
--- a/octavia_tempest_plugin/config.py
+++ b/octavia_tempest_plugin/config.py
@@ -148,6 +148,9 @@
                       'dict. Example: {"compute_zone": "The compute '
                       'availability zone."}'),
                 default={'compute_zone': 'The compute availability zone.'}),
+    cfg.IntOpt('listener_conn_limit',
+               default=200,
+               help='Defines listener connection limit.'),
     # Networking
     cfg.BoolOpt('test_with_ipv6',
                 default=True,