feat!: add model parameter on model hooks run on sequelize if they don't have an instance, add afterCount

[ephys]

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Description Of Change

Closes #16851

Model hooks also run on the Sequelize instance. Some of them include the model instance the hook runs on, but some of them don't have such an instance to include.

I added the model class to them instead.

This would be a breaking change because the model was added as the first parameter, to make them behave similarly to the instance parameter of other model hooks.

This PR also adds the afterCount hook.

First draft before I add all tests in case this change is a no-go in its current state

TODO

• Document which hooks receive the model
• Document afterCount
• Add hook tests

[ephys]

Thinking about this more:

• We should give the model definition, not the model itself, so this can be compatible with repository mode in the future
• Because of this, we could expose the class that the model definition is attached to on the ModelDefinition class
• I think we should give the ModelDefinition on all hooks, also to make it easier for repository mode users. I propose to add it as the last parameter of all model hooks. This would also simplify the typings.