feat: Move the SLA filter dropdown to UI folder (#9502)

# Pull Request Template

## Description

I moved the newly created SLA filter dropdown to the UI folder to use in
adding the Linear issue modal.

app/javascript/dashboard/components/ui/Dropdown/DropdownEmptyState.vue

@@ -0,0 +1,15 @@
+<script setup>
+defineProps({
+  message: {
+    type: String,
+    default: '',
+  },
+});
+</script>
+<template>
+  <div
+    class="flex items-center justify-center h-10 text-sm text-slate-500 dark:text-slate-300"
+  >
+    {{ message }}
+  </div>
+</template>