Add documentation to LinAlgError exception

[antonwolfy]

The PR adds missing docstrings to dpnp.linalg.LinAlgError exception.

• 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_10 ran successfully.
Passed: 1227
Failed: 0
Skipped: 9

[coveralls]

coverage: 72.015%. remained the same
when pulling 53cf97b on add-doc-to-LinAlgError-exception
into c27aae9 on master.

[vlad-perevezentsev]

LGTM!
Thank you @antonwolfy