Add checkbox based multiselect util component

Takes an array of objects (name, checked, description) and turns it into
a list of checkboxes, one for each element

frontend-reactive/app/components/util/multiselect.ts

@@ -0,0 +1,21 @@
+import { action } from '@ember/object'
+import Component from '@glimmer/component'
+
+export interface UtilMultiselectSignature {
+  // The arguments accepted by the component
+  Args: {
+    elements: Array<{ name: string; checked: boolean; description: string }>
+  }
+  // Any blocks yielded by the component
+  Blocks: {
+    default: []
+  }
+  // The element to which `...attributes` is applied in the component template
+  Element: null
+}
+
+export default class UtilMultiselect extends Component<UtilMultiselectSignature> {
+  @action onChange() {
+    console.log(this.args.elements)
+  }
+}