title: Replace the value in appSettings key without making multiple web.config files
body: <p>I have a key in appSettings of web.config file as follows:</p>
  
  <pre><code>&lt;appSettings&gt;
    &lt;add key="connectionString" value="my_dev_connectionString"/&gt;
  &lt;/appSettings&gt;
  </code></pre>
  
  <p>and I want to replace this value in Production Environment with "my_production_connectionString" but I DO NOT want to create multiple web.config files like web.test.config and web.production.config. 
  How do i do that?
  Is there a way I can replace this value in the Release definitions of the Visual Studio project?</p>