Encrypted matrix multiplication with plain vector

[philomath213]

Description

• Introduce Encrypted matrix multiplication with plain vector.
• The matrix should be padded with zeros (each row size need to be a power of two).
• The matrix should be encoded into a CKKS vector with vertical scan (column major).
• The matrix multiplication assumes that the matrix is encoded as I mentioned above, the plain vector should be also padded with zeros to the next power of two.
• There's a helper function to pad and encode the matrix, the resulting CKKS vector can do only Encrypted matrix multiplication with plain vector operation, but the result of this operation is a regular CKKS vector.

Affected Dependencies

• None.

How has this been tested?

• Python tests with random values generated using numpy.

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

TODO

• find a better name for functions.

[youben11]

LGTM!