Move commonly used response schemas out of _common.yaml into _common.responses.yaml

[nhtruong]

Coming from #489

A lot of OpenSearch responses are generic responses and have common schemas. For example, the ml.delete_model_group and ml.delete_model both use WriteResponseBase for their 200 response schema. However, contributors are most likely not aware of these popular schemas and will redefine these response schemas for the namespace they are working on.

I propose that we move these schemas into their own _common.responses.yaml file and highlight it in the DEV GUIDE.