Add a workflow to run nightly tests

[antonwolfy]

The PR proposes to add a workflow which runs nightly and includes installing dpnp from dppy/label/dev and running tests. It will cover both Linux and Windows.
This PR ensures tests are run even if no development happens. The intent is it might catch issues due to external dependency updates, and such.

The workflow can also be triggered manually.

• Have you provided a meaningful PR description?
• Have you added a test, reproducer or referred to 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?
• If this PR is a work in progress, are you filing the PR as a draft?

[github-actions]

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

[vtavana]

Thank you, @antonwolfy!