fix(editor): Allow overriding theme from query params (#7591)

Allow overriding theme through query params.. to be able to override it
from preview iframe in webcomponent

Github issue / Community forum post (link here to close automatically):

cypress/pages/demo.ts

@@ -0,0 +1,21 @@
+/**
+ * Actions
+ */
+
+export function vistDemoPage(theme?: 'dark' | 'light') {
+	const query = theme ? `?theme=${theme}` : '';
+	cy.visit('/workflows/demo' + query);
+	cy.waitForLoad();
+	cy.window().then((win) => {
+		// @ts-ignore
+		win.preventNodeViewBeforeUnload = true;
+	});
+}
+
+export function importWorkflow(workflow: object) {
+	const OPEN_WORKFLOW = {command: 'openWorkflow', workflow};
+	cy.window().then($window => {
+		const message = JSON.stringify(OPEN_WORKFLOW);
+		$window.postMessage(message, '*')
+	});
+}