title: Use semver or a timestamp in gitlab piplelines
body: <p>I'm using GitLab pipelines and have defined my build defintion in the <code>.gitlab-ci.yml</code> file.</p>
  
  <p>I'm using this to build docker containers.</p>
  
  <p>Simple question. Is there a way I can tag my docker containers with either a semver from gitlab or a timestamp.</p>
  
  <p>The build-in variables don't seem to give me much to work with.</p>
  
  <p>On Windows I've been able to use <code>GitVersion</code> before in powershell that gets the semver tag and puts it into a variable you can use in the rest of the build process.</p>
  
  <p>If I can't do that, is it possible to get a timestamp from the OS and use that in the yml file?</p>