[INS-159] simplify the two-tier model and model instance structure

[xiaofei-du]

Is your feature request related to a problem?

The current design of model and model instance is clumsy. Check the doc here.

• A model can have multiple model instances.
• A model does not have state.
• A model instance, as a second-tier resource, must belong to a model.
• A model instance has state.

But

• A model can't be a component of a pipeline.
• A model instance is the core component of a pipeline.

For users who are not familiar with ML/AI or are new to VDP, it is difficult to understand the relationships between these resources and the concept of a model instance is the instantiation of a model.

Describe the solution you'd like

We simplify model and model instance into a flat model structure.

Let me use importing yolov7 from instill-ai/model-yolov7-dvc repo as an example. When the model is imported (e.g., GitHub):

With the current model and model instance design, there will be one model that has two model instances

• model: yolov7
  • instance: v1.0-cpu
  • instance: v1.0-gpu

With the new model structure, there will be two models

• model: yolov7-v1-0-cpu
• model: yolov7-v1-0-gpu

With the new flat design,

• There is no model instance concept any more.
• A model is the core component of a pipeline.

_{From SyncLinear.com | INS-159}