Editor: Add example usage for getCurrentPostId selector

[SainathPoojary]

What?

Related issue: #42125
Related PR: #1062

This PR adds a missing JSDoc @example comment to the getCurrentPostId selector,

Why?

To improve developer documentation and maintain consistency with other selectors that include usage examples. The @example demonstrates how to properly use the getCurrentPostId selector with the useSelect hook

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Co-authored-by: SainathPoojary <sainathpoojary@git.wordpress.org>
Co-authored-by: Mamaduka <mamaduka@git.wordpress.org>

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[Mamaduka]

@SainathPoojary, the related issue/PR points to the same link.

P.S. I think @ryanwelcher was also working on something similar. I think, once someone knows how the useSelect hook works, those examples won't be beneficial.

[SainathPoojary]

Thanks for pointing it out, @Mamaduka . I’ve updated the PR description, the correct related issue is #42125.