fix: Port model_obb to canRotate

[galou]

Moreover, model_obb defaulted to false, whereas canRotate defaults to true.

[galou]

Any comment?

[makseq]

There are two issues with this PR:

1. By default, canRotate=true in most labeling configurations, but canRotate is usually omitted from these configurations. Most users employ a simple model of bounding boxes from YOLO. So, if canRotate is used instead of model_obb, the default value should be set to true. Exactly this was done at this line -https://github.com/HumanSignal/label-studio-ml-backend/pull/650/files#diff-e618adcb4b8dc30994387450f5fd296a819c048170545f8801bdb7fda5e0ecdcL15, but it will disrupt existing projects for nearly all users who use simple bounding boxes without obb. (This was the reason why model_obb was introduced instead of using canRotate).
2. This PR eliminates backward compatibility, causing all users who currently use model_obb in their label configurations to experience broken projects.

[galou]

Ok, so I guess I can close the PR.