* [PM-17562] Refactor event integration methods / declarations in ServiceCollectionExtensions
* Refactored ServiceCollectionExtensions to use TryAdd and still launch unique listeneer services
* Updated unit tests to match new generic format for Listeners
* Fix method spacing
* Update README to reflect new integration setup in ServiceCollectionExtensions
* Move interfaces to I prefix; fix typo in subscription
* Fix reference to IIntegrationListenerConfiguration