The exception was incorrectly marked as 'KeyError', but enum throw
'ValueError' instead.

Previously we would have the exceptions making debugging quite harder.

When requesting '--debug', it seems ok to show the stack trace that
created the error

This improves the consistency of our error reporting

This allows removing completely the '_node_get_option_str' on context
and ensures every method relying on a few set of keys set their errors
consistently

Also add helpers for the cli to be able to represent 'FastEnum' directly

This adds a method to ensure that a value is from a set of valid values
and raises an error message accordingly.

- Define Enum types for each of the relevant cases
- Adapt call places that were doing such things manually

This allows for stronger guarantees when checking the level of
consistency since it will only be comparable with itself, and ensures
unicity

'Enum' has a big performance impact on the running code. Replacing
it with a safe subset of functionality removes lots of this overhead
without removing the benefits of using enums (safe comparisions,
uniqueness)

Changes made to allow artifact checkout/push/pull to take
artifact references as well as element names.
Added test to ensure this works