Add get_page_by_template function to retrieve page by template

[gustavocoimbradev]

This contribution implements a new function that retrieves the ID or permalink of a page based on its assigned template. The function performs a query to find pages using a specific template and returns either the ID or permalink of the first matching page.

Trac ticket: https://core.trac.wordpress.org/ticket/62666

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[github-actions]

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[github-actions]

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[github-actions]

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