title: Add custom properties to Serilog
body: <p>I'm using Serilog with an MS SQL Server sink in my application. Let's assume I have defined the following class ...</p>
  
  <pre><code>public class Person
  {
    public string FirstName { get; set; }
    public string LastName { get; set; }
  
    public DateTime BirthDate { get; set; }
    // ... more properties
  }
  </code></pre>
  
  <p>... and created an instance:</p>
  
  <pre><code>var person = new Person
  {
      FirstName = "John",
      LastName = "Doe",
      BirthDate = DateTime.UtcNow.AddYears(-25)
  };
  </code></pre>
  
  <p>I have placed the following log call in my code:</p>
  
  <pre><code>Log.Information("New user: {FirstName:l} {LastName:l}",
      person.FirstName, person.LastName);
  </code></pre>
  
  <p>Is it possible to also log the <code>BirthDate</code> property <em>without adding it to the message template</em> so that it's rendered within the <code>Properties</code> XML column? I'd like to output it later in a details view of my application's log viewer.</p>
  
  <p>I'm basically looking for a behavior similar to the object destructuring, but without printing the flat object as part of the log message.</p>