This allows us to get rid of some of the validation in sanity_checks()
as mypy handles this validation at "build time", and any typos in the
enum instantiation would be a runtime error rather than a silent
failure.
Additionally, it allows us to encode some of the behaviour of the
different output types into the type definition itself by using methods.
Part-of: https://gitlab.postmarketos.org/postmarketOS/pmbootstrap/-/merge_requests/2642
(cherry picked from commit 7d2f055bcb)
pmb: Fix PmbArgs containing a string for output
While the annotations were changed to suggest that the output property
of PmbArgs contains a RunOutputType, at runtime it actually contained a
string because the argument parsing code hadn't been adapted to create a
RunOutputType. Fix this, and also change it to RunOutputTypeDefault as
while at it as that's more accurate.
Fixes 7d2f055bcb
7fcbcdc19c