Optimistic locking example is missing from the model configuration docs [v6]

[johnmatthiggins]

Issue Description

There is no example of optimistic locking in the documentation.

What was unclear/insufficient/not covered in the documentation

There isn't really any documentation about using the version property to enable optimistic locking. There's a page on optimistic locking that links to the model configuration page. However, the model configuration page doesn't actually contain any details about how to implement optimistic locking in your sequelize schema. This used to be documented in v5 but it seems like after the docs were restructured this was thrown out.

If possible: Provide some suggestion on how we can enhance the docs

Add in the information for configuring optimistic locking back in to the model configuration docs.

Additional context

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