title: Add a field with value to all existing Solr documents
body: <p>I want to add a field with value to all my existing Solr documents. I was searching a lot online but can't find a clear way to do it. I need to be able to search/filter documents by that field as well.</p>
  <p>Edit: Added clarification - I want to update all existing documents with this new field and value as well.</p>