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
(cherry picked from commit 81344d251fd7ac1e34d6e8927a494a554ec81b24)
diff --git a/octavia_tempest_plugin/config.py b/octavia_tempest_plugin/config.py
index c40293c..b313471 100644
--- a/octavia_tempest_plugin/config.py
+++ b/octavia_tempest_plugin/config.py
@@ -151,6 +151,9 @@
                       '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,