Add Customizer Field for Google Search Engine ID on Phonebook Page

[Ramin-Farhadi]

Description
We want to add a field in the Customizer called "phonebook," where we can specify the Google ID.

Why It's Important
Since we're using the Programmable Search Engine on the /phonebook page, we need to assign a Google ID to load the search toolbar. By adding this feature to the Customizer, we can change the search engine by simply updating the ID there, instead of modifying the theme each time.