Make the transpiler arguments agnostic

[lars-petter-hauge]

Currently the transpiler has hardcoded both keys (i.e. python-version and rhel) and values (3.8 and 7 respectively), the latter will be added as a command line option in #308. However, the setup should really be agnostic of the keys.

E.g, one could consider the following specification in this valid release file:

a: 0.0.1
b:
  rhel-7: 0.0.1
  rhel-8: 0.0.2
c:
  py-2:
    rhel-7: 0.0.1
    rhel-8: 0.0.2
  py-3: 0.0.3

Currently it is valid because the py and rhel prefix is hardcoded. But it is possible to determine these keys by looking at the file itself. Hence it should be possible to have the transpiler unaware of the names of the keys.

The arguments entered when using the transpiler could be for instance rhel: 7 py: [2,3] (click sort of supports key,val. Have not looked into it a lot..).