feat(ske): port to v2api version of SDK

[MichaelEischer]

Description

Adapt the SKE commands to the latest sdk version, which includes the API changes for #1328 .

There is one slight behavior change though: decoding into CreateOrUpdateClusterPayload for the ske cluster create or ske cluster update commands now returns an error if an unknown field is set in the input. This is probably a good idea, but is probably noteworthy. A possibly common cause of this problem is using stackit ske cluster describe -ojson to dump the cluster config, modify it and update it using stackit ske cluster update. Now, instead of describe the stackit ske cluster generate-payload command has to be used.

Checklist

• Issue was linked above
• Code format was applied: make fmt
• Examples were added / adjusted (see e.g. here)
• Docs are up-to-date: make generate-docs (will be checked by CI)
• Unit tests got implemented or updated
• Unit tests are passing: make test (will be checked by CI)
• No linter issues: make lint (will be checked by CI)