* Add ActiveMQ Docker logging config for development
* Add ClientIndividualConsumer and ClientIndividualListener. These classes allow:
  * create a listener per connection, to avoid one listener instance shared among all threads
  * each listener to call ack/nack in their connection
  * cleanup connections list (was growing forever, every 5 minutes appending new connections)
* Catch BrokenPipeError, until stomp.py has a proper fix to the race condition. Provided a [MR](https://github.com/jasonrbriggs/stomp.py/issues/393).
* Upgrade from centos stream 8 to centos stream 9
* Bump python 3.6 (EOL was 23 Dec 2021) to 3.9 (EOL 05 Oct 2025)
  * Replace `pycrypto` (unmaintained, obsolete, and contains security vulnerabilities.) with `pycryptodome`
* Log thread_id in all logs
* Make Auditing a class instance, property of the processor instance
* Share SQLAlchemy engine and connection pooler (set as a class property, protected by a lock) to avoid multiple calls to automap_base which would throw a SA warning
* Retry etcd client on external disconnect/ failure to create client
* Fix typo: Uppercase priority coming in email gateway

Merge branch '54-sign-outgoing-mails-smime' of https://gitlab.cern.ch/push-notifications/notifications-consumer into 54-sign-outgoing-mails-smime