Req: display custom text when query returns no result

I'd like to be able to display a custom message when there is no search-result

Something like (simplesearch_results.html.twig)

```
{% if query %}
{% set count = search_results ? search_results.count : 0 %}
{% if count is same as( 0 ) %}
{{ "PLUGIN_SIMPLESEARCH.SEARCH_NORESULTS"|t(query|e, count)|raw }}
{% elseif count is same as( 1 ) %}
{{ "PLUGIN_SIMPLESEARCH.SEARCH_RESULTS_SUMMARY_SINGULAR"|t(query|e)|raw }}
{% else %}
{{ "PLUGIN_SIMPLESEARCH.SEARCH_RESULTS_SUMMARY_PLURAL"|t(query|e, count)|raw }}
{% endif %}
% endif %}
```

Start with simplesearch_results.html.twig, the template named in the issue, and inspect how query and search_results are currently rendered. Confirm how translation keys are defined in the plugin, then verify that a zero-result query displays the requested custom translated message while existing singular and plural result summaries remain unchanged.

Written by the indexing model from the issue text.