Update empty search guidelines

What does this MR do?

We added some documentation around empty search results recently in #1210 (closed). I realized it doesn't always work for empty search use cases since sometimes there are filters applied (using the filter component), rather than a simple search (using the search component). I audited the cases of empty results from filters vs search components and found that we do not consistently provide messages as to why there were no matches. So I'm proposing to split the messages so that directly apply to either a search or filter.

Relates to #1224 (closed)

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