Detect possible misplaced boolean on command line

What does this MR do?

We know our CLI library gets mad about boolean, this leads to frequently duplicated issues about broken config agter gitlab-runner register.

This simple patch tries to warn the user about the correct usage of boolean flags.

$ ./gitlab-runner register -n --executor docker --docker-tlsverify false 
WARNING: boolean parameters must be passed in the command line with --docker-tlsverify=false
WARNING: parameters after this may be ignored   

...execution continue

Does this MR meet the acceptance criteria?

• Documentation created/updated
• Tests
  • Added for this feature/bug
  • All builds are passing
• Branch has no merge conflicts with master (if you do - rebase it please)

What are the relevant issue numbers?

#3360 (closed)