Gracefully handle item types that we don't cover

[wjohnson]

Describe the feature
We should be able to handle new item types without throwing errors in Needlr. As a new item comes along, users should be able to still manage things like listing the objects in a workspace.

Detailed Example
For example, we currently do not support Apache Airflow Jobs. I receive an exception when trying to list all items in a workspace that contains an airflow job.

Issues that this feature solves
First time seeing this issue.

Suggested Implementation
I'm thinking we need to have an "UnhandledItemType" in Pydantic that just tries its best to extract things like display name, type, and then shoves all of the remaining content into a field like json.

Additional context
N/A