[cli] add support to spawn multiple workers of the same type

Also, added `worker run-single-job` because the `run-single` option
was a bit confusing.
4 jobs for dev-support-concurrent-workers in 49 minutes and 16 seconds (queued for 10 minutes and 25 seconds)
latest
Status Job ID Name Coverage
  Cabal
passed #19166
cabal

00:22:23

 
  Stack
passed #19167
stack

00:02:21

 
  Bench
manual #19168
allowed to fail manual
bench
 
  Test
passed #19169
test

00:24:31