[UI] revert index.html base url and provide USE_AWS_INSTANCE_PROFILE example (#2403)

* revert index.html base url and provide USE_AWS_INSTANCE_PROFILE example

ui/operator_ui/main.py

@@ -311,7 +311,7 @@ def send_js(path):
 @app.route('/')
 @authorize
 def index():
-    return render_template('index.html', google_analytics=GOOGLE_ANALYTICS, app_url=APP_URL)
+    return render_template('index.html', google_analytics=GOOGLE_ANALYTICS)
 
 
 DEFAULT_UI_CONFIG = {

ui/operator_ui/templates/index.html

@@ -2,7 +2,6 @@
 <html lang="en">
   <head>
     <meta charset="utf-8">
-    <base href="{{app_url}}">
     <title>PostgreSQL Operator UI</title>