feature flag to allow allow changing of '.' to '_' in the normalize_symbol function

[ITJamie]

when using some swagger apis the operationid can have long paths (example ) eg "operationId": "cmk.gui.plugins.openapi.endpoints.notification_rules.show_rules",

this was creating service functions with slightly unreadable names: eg:def cmkguipluginsopenapiendpointsnotification_rulesshow_rules

by patching openapi_python_generator/language_converters/python/common.py function normalize_symbol and adding symbol = symbol.replace(".", "_") we get a saner function name of: def cmk_gui_plugins_openapi_endpoints_notification_rules_show_rules

while this change might not be what most people want. having a toggle for it would be quite useful