Add support for '-1' as version

[mattieserver]

About this change - What it does

This allows adding '-1' as the version just like 'latest'.

References: #668

Why this way

This seems like the quickest way to add support for the '-1'

[jjaakola-aiven]

This is the easiest way to add the -1 support. I'd prefer to move the responsibility of resolving to a Version class and the validation of the input string closer to the REST API. That would mean a bit more of refactoring:

• Move karapace.typing.Version to karapace.schema_models.Version
• Change to a class and implement the resolving and validation.
• Change the _resolve_version calls version.resolve(schema_versions).
• Create the version objects from the input string in karapace.schema_registry_api.
• Add tests

[mattieserver]

I expected something like this 😄

I try to implement the changes like you requested.

[aiven-anton]

This should possibly be kept in sync with the respective handling here:

karapace/karapace/schema_reader.py

Line 572 in 4ab7e9e

reference = reference.resolve(max(subject_data))