spa-pod: add the ability to specify Id properties as strings

Use the unused 'K' format letter in the varargs builder & parser methods
2 jobs for spa-type-refactoring in 1 minute and 12 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Container
passed #6680805
container_fedora

00:00:15

 
  Build
passed #6680806
build_on_fedora

00:00:56