Make debug option of wsgi server configurable

Because in some deployments tracebacks in API responses are unwanted
for security reasons.

Change-Id: I8a2acea7393c369bfa7d7822f21b4d40d56d6739
Needed-By: https://review.opendev.org/c/openstack/neutron/+/818391
Partial-Bug: #1951429

oslo_service/_options.py

@@ -88,6 +88,11 @@ wsgi_opts = [
                     "If an incoming connection is idle for this number of "
                     "seconds it will be closed. A value of '0' means "
                     "wait forever."),
+    cfg.BoolOpt('wsgi_server_debug',
+                default=False,
+                help="True if the server should send exception tracebacks to "
+                     "the clients on 500 errors. If False, the server will "
+                     "respond with empty bodies."),
     ]
 
 ssl_opts = [

oslo_service/wsgi.py

@@ -180,7 +180,7 @@ class Server(service.ServiceBase):
             'custom_pool': self._pool,
             'log': self._logger,
             'log_format': self.conf.wsgi_log_format,
-            'debug': False,
+            'debug': self.conf.wsgi_server_debug,
             'keepalive': self.conf.wsgi_keep_alive,
             'socket_timeout': self.client_socket_timeout
             }

releasenotes/notes/add-wsgi_server_debug-opt-70d818b5b78bfc7c.yaml

@@ -0,0 +1,7 @@
+---
+features:
+  - |
+    A new config options, ``[DEFAULT] wsgi_server_debug``, has been added.
+    This allows admins to configure whether the server should send exception
+    tracebacks to the clients on HTTP 500 errors. This defaults to ``False``,
+    preserving previous behavior.