title: How to rename a tag in Azure DevOps
body: <p>We have a large instance of Visual Studio Online or VSTS or Azure DevOps.
  We have a Tag on work items that is called "A B" for example. Someone also 
  created another tag "AB". I want to just rename the tag "A B" to "Don't use A B" or 
  just delete the tag if possible. Is there an API I could use to do this?
  I checked out the TAGHelper add-in but because we have many tags, the tag helper add-in is just unusable. I can write a simple tool if needed, but wondering if there is a quick way to do this.</p>