Regex support on When its key has value

[eerkunt]

This PR will adds four new steps for supporting regular expression matching on some of the When directives ;

  When its {key} is "{regex pattern}" regex
  When its {key} is not "{regex pattern}" regex
  When its {key} metadata has "{regex pattern}" regex
  When its {key} metadata has not "{regex pattern}" regex

along with all the combinations.