Refactor the CLI model registry client once MR supports proper REST status codes

[devguyio]

Description

The Model Registry currently does not follow the REST standard status codes (e.g., 404 for non-existing resources). Instead, it returns 500, and the error details are in the response. Some custom error checking was used in the cli modelregistry client.

However, model registry is planning to change that and support standard REST status codes, see opendatahub-io/model-registry-bf4-kf#305 .

Once that's implemented, the modelregistry client will need to be refactored to check those status codes.