Add stateful test endpoint for Notification acceptance tests

Description:

Issue:

• in the Register service we have a testing endpoint that does not have any state and cannot provide meaningful responses.
• To test Notification service functionality we need a way to verify that events are actually delivered.

Solution:

Stateful test endpoint for Notification acceptance tests added: notification!557 (merged)

How to test:

Does functionality was tested and how?

Changes include:

• Refactor (a non-breaking change that improves code maintainability).
• Bugfix (a non-breaking change that solves an issue).
• New feature (a non-breaking change that adds functionality).
• Breaking change (a change that is not backward-compatible and/or changes current functionality).

Changes in:

• Common code

Dev Checklist:

• Added Unit Tests, wherever applicable.
• Updated the Readme, if applicable.
• Existing Tests pass
• Verified functionality locally
• Self Reviewed my code for formatting and complex business logic.

Other comments:

Any comments to approvers here