Feature/wpce 330 algolia autocomplete debounce

[daveromsey]

Closes https://webdevstudios.atlassian.net/browse/WPCE-330

• Adds single setting for Algolia Autocomplete debounce timeout with a default to zero, for disabled.
• Adds filters to allow for the debounce value to be set individually for each index.

Here's a plugin to test overriding the debounce timeout value for the searchable_posts index.

<?php
/**
 * Plugin Name:       Algolia Test Site Functions
 * Plugin URI:
 * Description:
 * Version:           1.0.0
 */

namespace AlgoliaTestFunctions;

add_filter( 'algolia_autocomplete_debounce_wp_searchable_posts', __NAMESPACE__ . '\searchable_posts_index_debounce' );
function searchable_posts_index_debounce() {
    return 5000;
}