Unified API: Better Error Messages

[Prajna1999]

Describe the current behavior
Error messages are not self explanatory and generic

Describe the enhancement you'd like
Pinpointed error messages that would be easier to debug.

Why is this enhancement needed?
Better debuggability

Additional context
Example
POST /config 422 error

"Failed at kaapi_uuid: %{status: 422, body: %{error: \"('body', 'config_blob', 'completion', 'NativeCompletionConfig', 'provider'): Input should be 'openai-native' or 'google-native'\\n('body', 'config_blob', 'completion', 'NativeCompletionConfig', 'type'): Field required\\n('body', 'config_blob', 'completion', 'function-after[validate_params(), KaapiCompletionConfig]', 'type'): Field required\", data: nil, metadata: nil, success: false}}"