title: Set connection string in Azure DevOps pipeline
body: <p>I have some integration tests that I'd like to run against LocalDB.</p>
  
  <p>My config.json file has the following section...</p>
  
  <pre><code>{
    "ConnectionStrings": {
      "DefaultConnection": ""
    }
  }
  </code></pre>
  
  <p>Is it possible to set this value in the build config?</p>