[Python][Client] Default to system CA instead of certifi (#8108)

* Use system CA by default and remove certifi

See https://github.com/OpenAPITools/openapi-generator/issues/6506

* Use system CA by default in asyncio client

* Update README_onlypackage.mustache

* Result of ./bin/generate-samples.sh

* Add ssl_ca_cert argument for Configuration

* Result of ./bin/generate-samples.sh

* Remove certifi, use system CA by default

samples/client/petstore/python-asyncio/petstore_api/configuration.py

@@ -77,6 +77,8 @@ class Configuration(object):
     :param server_operation_variables: Mapping from operation ID to a mapping with
       string values to replace variables in templated server configuration.
       The validation of enums is performed for variables with defined enum values before.
+    :param ssl_ca_cert: str - the path to a file of concatenated CA certificates 
+      in PEM format 
 
     :Example:
 
@@ -125,6 +127,7 @@ conf = petstore_api.Configuration(
                  disabled_client_side_validations="",
                  server_index=None, server_variables=None,
                  server_operation_index=None, server_operation_variables=None,
+                 ssl_ca_cert=None,
                  ):
         """Constructor
         """
@@ -193,7 +196,7 @@ conf = petstore_api.Configuration(
            Set this to false to skip verifying SSL certificate when calling API
            from https server.
         """
-        self.ssl_ca_cert = None
+        self.ssl_ca_cert = ssl_ca_cert
         """Set this to customize the certificate file to verify the peer.
         """
         self.cert_file = None

samples/client/petstore/python-asyncio/petstore_api/rest.py

@@ -17,7 +17,6 @@ import re
 import ssl
 
 import aiohttp
-import certifi
 # python 2 and python 3 compatibility library
 from six.moves.urllib.parse import urlencode
 
@@ -51,14 +50,7 @@ class RESTClientObject(object):
         if maxsize is None:
             maxsize = configuration.connection_pool_maxsize
 
-        # ca_certs
-        if configuration.ssl_ca_cert:
-            ca_certs = configuration.ssl_ca_cert
-        else:
-            # if not set certificate file, use Mozilla's root certificates.
-            ca_certs = certifi.where()
-
-        ssl_context = ssl.create_default_context(cafile=ca_certs)
+        ssl_context = ssl.create_default_context(cafile=configuration.ssl_ca_cert)
         if configuration.cert_file:
             ssl_context.load_cert_chain(
                 configuration.cert_file, keyfile=configuration.key_file