This new module contains utilities that help to introspect parts
that constitute the inner parts of osbuild, i.e. its stages
and assembler (which is also considered a type of stage in
this context). It contains the `StageInfo` class that can that
contains meta-information about the individual stage, such as
a short information (`info`), a longer description (`desc`) and
its JSON schema. A new Schema class represents schema data and
has a `validation` method that can be used to validate that json
data conforms to said schema.
A `Index` class can be used to obtain `StageInfo` and `Schema`
for entities identified via `klass` and `name`.
A top level `validate` method is introduced that can validate
manifest data.
Internally it uses the `jsonschema` package so add that as a
requirement and Install this dependency in the CI.
