Improve async logic to scale better

[switschel]

Currently some async logic is implemented e.g. processing Messages are mainly done async. Still, the code blocks executed asynchronously contains too much logic.

To better scale the Dispatchers should be optimized in not only calling processMessage asynchronously but also other methods.
For example:

1. Thread receives the messages --> forward to dispatcher
2. Thread process the message by replacing substitutes
3. ...
4. Sends the message to C8Y or outbound to Connector

Every "heavy" and cpu-intensive processing should be handled asynchronously if possible.

[switschel]

This issue will be addressed with the upcoming Spring Boot 3.0.x update and leverage Virtual Threads.
We already implemented something in the following branch https://github.com/Cumulocity-IoT/cumulocity-dynamic-mapper/tree/virtualThreads but waiting for the "new" Microservice SDK is released so we can officially use Virtual Threads.