Interactivity API Docs: Add server functions documentation.

[cbravobernal]

What?

Add server functions to the Interactivity API reference docs.

[github-actions]

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[github-actions]

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Co-authored-by: c4rl0sbr4v0 <cbravobernal@git.wordpress.org>
Co-authored-by: fabiankaegy <fabiankaegy@git.wordpress.org>

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[fabiankaegy]

Love these updates :)