added multi_select_controller and added multi-select support for tags without Ctrl/Shift in transaction forms (#55)

* added multi_select_controller and added multi-select support for tags without Ctrl/Shift in transaction forms

* fix: prevent memory leak by properly cleaning up event listener in multi-select controller

* chore: updated indentation

app/javascript/controllers/multi_select_controller.js

@@ -0,0 +1,21 @@
+import { Controller } from "@hotwired/stimulus";
+
+export default class extends Controller {
+  connect() {
+    this.element.addEventListener('mousedown', this.toggleOption);
+  }
+
+  disconnect() {
+    this.element.removeEventListener('mousedown', this.toggleOption);
+  }
+
+  toggleOption = (e) => {
+    const option = e.target;
+    if (option.tagName === 'OPTION') {
+      e.preventDefault();
+      option.selected = !option.selected;
+      const event = new Event('change', { bubbles: true });
+      this.element.dispatchEvent(event);
+    }
+  }
+}