MG-165 is created to add the proposal of the time frame based Must Gather log size reduction. This ticket is the implementation part of the time frame based Must Gather log size reduction. 

Add the fields `since` and `sinceTime` in the `additionalConfig` struct of `MustGatherSpec` in the API. Implement the functionality to reduce the must gather log size. 

Check if the env variables MUST_GATHER_SINCE and MUST_GATHER_SINCE_TIME needed to be added in the must gather collection scripts other than 
get_log_collection_args. 
Create unit tests cases and make sure code coverage is met.