Update docstrings for counting functions

[antonwolfy]

The PR updates docstrings for counting functions to have a blank line prior Default value.

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[github-actions]

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

[github-actions]

Array API standard conformance tests for dpnp=0.18.0dev0=py312he4f9c94_23 ran successfully.
Passed: 1006
Failed: 0
Skipped: 17

[vlad-perevezentsev]

Thank you @antonwolfy !

[coveralls]

coverage: 71.952%. remained the same
when pulling 7538c67 on update-counting-docstrings
into edf2dbf on master.