Set initial time window size of the micro simulation in the configuration

[IshaanDesai]

This PR implements changes which allow for the user to set the initial time window size (dt) of the micro simulation during configuration. The time window size is then using in the coupling, which allows for subcycling.

Note: The micro simulation cannot modify the time window size during the coupling. A followup feature can change the micro simulation library API in a way that the solve(...) function call can return the desired time step value of the micro simulation.

Checklist:

• I made sure that the CI passed before I ask for a review.
• I added a summary of the changes (compared to the last release) in the CHANGELOG.md.
• If necessary, I made changes to the documentation and/or added new content.
• I will remember to squash-and-merge, providing a useful summary of the changes of this PR.

[BenjaminRodenberg]

@IshaanDesai Anything specific where you would need feedback? It's a bit hard for me to give a general review here because I'm not that much involved in this project.