You’d want to use a plugin-outlet for this, discovery-list-container-top would work.
<script type="text/x-handlebars" data-template-name="/connectors/discovery-list-container-top/custom-name">
<button> your button here </button>
</script>
It would just take a bit of additional CSS to align it to the right instead of the left.
There’s more on handlebars templates and plugin outlets in Developer’s guide to Discourse Themes