Add cross-reference fallback for dpnp.tensor to dpctl 0.21.1 docs

[vlad-perevezentsev]

This PR proposes to replace dpctl.tensor with dpnp.tensor across the error messages.
Add a Sphinx handler to redirect dpnp.tensor.* cross-references to dpctl 0.21.1 docs
and tensor.rst page linking to the dpctl API reference

• Have you provided a meaningful PR description?
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• 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

[coveralls]

Coverage is 77.879% — update_error_messages into include-dpctl-tensor. No base build found for include-dpctl-tensor.

[github-actions]

Array API standard conformance tests for dpnp=0.20.0dev6=py313h509198e_63 ran successfully.
Passed: 1355
Failed: 5
Skipped: 16