Fix model type for classification

[robiscoding]

Description

• Classification inference requests don't have a null model_type which is causing downstream issues in Model Monitoring (missing label/misreporting)
• This change manually sets the classification model type and adds some unit tests

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• This change requires a documentation update

How has this change been tested, please provide a testcase or example of how you tested the change?

• Tested that classification projects have a defined model_type when making a legacy infer request and checking the item in a local cache
• Added unit tests for the serializers file

Any specific deployment considerations

For example, documentation changes, usability, usage/costs, secrets, etc.

Docs

• Docs updated? What were the changes: