Implementing VectorSumCombiner

[rialg]

Description

Following the first item described in #264, this PR has the implementation of the VectorSumCombiner class, which should be used to compute vector/array sums.

Affected Dependencies

Needed to extend AggregateParams with the fields norm_kind and max_norm.

How has this been tested?

• Tests added to combiners_test.py

==================================================================================================================== test session starts =====================================================================================================================
platform linux -- Python 3.9.10, pytest-7.1.2, pluggy-1.0.0
plugins: timeout-2.1.0
collected 45 items                                                                                                                                                                                                                                           

tests/combiners_test.py .............................................                                                                                                                                                                                  [100%]

====================================================================================================================== warnings summary ======================================================================================================================
../.local/lib/python3.9/site-packages/hdfs/config.py:15
DeprecationWarning: the imp module is deprecated in favour of importlib; see the module's documentation for alternative uses
    from imp import load_source

-- Docs: https://docs.pytest.org/en/stable/how-to/capture-warnings.html
=============================================================================================================== 45 passed, 1 warning in 2.20s ================================================================================================================

Checklist

• I have followed the Contribution Guidelines and Code of Conduct
• I have commented my code following the OpenMined Styleguide
• I have labeled this PR with the relevant Type labels
• My changes are covered by tests

[dvadym]

Thank you! It looks good, I left comments

[dvadym]

Thank you! It looks great. Just a few minor comments

[dvadym]

Thank you!