Update licensing metadata

[antonwolfy]

The PR changes the license from BSD-2-Clause to BSD-3-Clause, so called the “New BSD License” or “Modified BSD License”.
Also that aligns the license used by MKL components or by NumPy.

The license header is updated with BSD-3-Clause per each impacted file in the repository.

• Have you provided a meaningful PR description?
• Have you added a test, reproducer or referred to an issue with a reproducer?
• Have you tested your changes locally for CPU and GPU devices?
• Have you made sure that new changes do not introduce compiler warnings?
• Have you checked performance impact of proposed changes?
• Have you added documentation for your changes, if necessary?
• Have you added your changes to the changelog?

[github-actions]

View rendered docs @ https://intelpython.github.io/dpnp/index.html

[github-actions]

Array API standard conformance tests for dpnp=0.20.0dev0=py313h509198e_8 ran successfully.
Passed: 1227
Failed: 0
Skipped: 9

[coveralls]

coverage: 72.098%. remained the same
when pulling 0858f85 on upgrade-license-to-new-bsd
into cb067e6 on master.

[xaleryb]

I checked with Jessica who is coordinating license change questions - she is approved that PR to be merged.