POC: replace our external log aggregation feature with rsyslog

- this change adds rsyslog (https://github.com/rsyslog/rsyslog) as
  a new service that runs on every AWX node (managed by supervisord)
  in particular, this feature requires a recent version (v8.38+) of
  rsyslog that supports the omhttp module
  (https://github.com/rsyslog/rsyslog-doc/pull/750)
- the "external_logger" handler in AWX is now a SysLogHandler that ships
  logs to the local UDP port where rsyslog is configured to listen (by
  default, 51414)
- every time a LOG_AGGREGATOR_* setting is changed, every AWX node
  reconfigures and restarts its local instance of rsyslog so that its
  fowarding settings match what has been configured in AWX
- unlike the prior implementation, if the external logging aggregator
  (splunk/logstash) goes temporarily offline, rsyslog will retain the
  messages and ship them when the log aggregator is back online
- 4xx or 5xx level errors are recorded at /var/log/tower/external.err

awx/main/management/commands/run_dispatcher.py

@@ -7,7 +7,6 @@ from django.core.cache import cache as django_cache
 from django.core.management.base import BaseCommand
 from django.db import connection as django_connection
 
-from awx.main.utils.handlers import AWXProxyHandler
 from awx.main.dispatch import get_local_queuename, reaper
 from awx.main.dispatch.control import Control
 from awx.main.dispatch.pool import AutoscalePool
@@ -56,11 +55,6 @@ class Command(BaseCommand):
         reaper.reap()
         consumer = None
 
-        # don't ship external logs inside the dispatcher's parent process
-        # this exists to work around a race condition + deadlock bug on fork
-        # in cpython itself:
-        # https://bugs.python.org/issue37429
-        AWXProxyHandler.disable()
         try:
             queues = ['tower_broadcast_all', get_local_queuename()]
             consumer = AWXConsumerPG(