Add debounce option to Autocomplete settings UI

[tw2113]

Much like we have hitsPerPage: config[ 'max_suggestions' ], and the config variable providing per-autocomplete index configurations, let's look into also doing the same with debounce.

It will need to be provided as milliseconds inside our algolia.autocomplete.sources.forEach(()=>{}) loop.

Also need to figure out, as best we can, what the closest to default is within the autocomplete library and use that as the default for the UI.

With us still working out how to best handle Autocomplete 1.x, making this UI item useful for that as well will be most beneficial.