Improve activemq connection handling
Follow up from: https://gitlab.cern.ch/push-notifications/backend/-/merge_requests/189
Seems like creating a connection per request is a big overhead.
Look into using Dependency injection or an ApplicationContext to inject just one activeMQ connection which supports reconnect.
Perhaps https://github.com/core-ts/activemq (wrapper around stompit
which we currently use) as inspiration