Detecting if a result is in the v1 format using DisallowUnknownFields was
clever. However, the format of v1 result changed in the worst way at some
point in the past: A field (id) got added. Therefore, this was an unknown
field to osbuild-composer and it fall back to decoding the input as a v2
result which led to empty logs.
This commit reimplements the result schema check: The new format always
have a top-level type field, whereas the old format doesn't have it. The
new implementation uses this fact to distinguish between v1 and v2 format
of a result.
Signed-off-by: Ondřej Budai <ondrej@budai.cz>
