chore: move server e2e tests to system-tests (#16354)

Co-authored-by: Brian Mann <brian.mann86@gmail.com>
Co-authored-by: Zach Bloomquist <git@chary.us>
Co-authored-by: Zach Bloomquist <github@chary.us>

system-tests/projects/plugins-async-error/cypress.json

@@ -0,0 +1 @@
+{}

system-tests/projects/plugins-async-error/cypress/integration/app_spec.js

@@ -0,0 +1,3 @@
+it('is true', () => {
+  expect(true).to.be.true
+})

system-tests/projects/plugins-async-error/cypress/plugins/index.js

@@ -0,0 +1,9 @@
+module.exports = (on) => {
+  on('file:preprocessor', () => {
+    return new Promise(() => {
+      setTimeout(() => {
+        throw new Error('Async error from plugins file')
+      }, 50)
+    })
+  })
+}