Introduce envsubst for config.js, update deps (#3032)

This is the implemenation of envsubst discussed in #1756 

Documentation update will follow after merge.

tests/e2e/template_spec.js

@@ -0,0 +1,15 @@
+const helpers = require("./helpers/global-setup");
+
+describe("templated config with port variable", () => {
+	beforeAll(async () => {
+		await helpers.startApplication("tests/configs/port_variable.js");
+	});
+	afterAll(async () => {
+		await helpers.stopApplication();
+	});
+
+	it("should return 200", async () => {
+		const res = await helpers.fetch("http://localhost:8090");
+		expect(res.status).toBe(200);
+	});
+});