[SYSTEMDS-2550] Batch scaling and weighing of imbalanced workers

[tobiasrieger]

This PR provides a number of updates to the Federated Parameter Server

• Batch Scaling to fix imbalance during runtime
• Weighing of gradients relative to the data size the represent for all runtime balancing schemes
• Seeding for data partitioners
• New test cases and better logging

[sebwrede]

It generally looks good, I added a few comments.

It could make sense to add documentation to each of the subclasses of DataPartitionFederatedScheme describing the partitioning scheme the class represents. This would make it easier to quickly understand the differences between the partitioning scheme classes, which would make it easier for you to present your work and it would be easier for future development/review of the classes.

[tobiasrieger]

@sebwrede I have addressed all other proposed changes in the new commit. Thanks!

[sebwrede]

LGTM!

[mboehm7]

LGTM - thanks @tobiasrieger for the patch and @sebwrede for the review. I only modified some formatting issues, reduced the visibility of some members, change the string concatenation, and guarded the info logging (to avoid unnecessary string concatenation).