Query table with 3 associations

Issue Description

What was unclear/insufficient/not covered in the documentation

The docs covered several M:N scenarios, but could not find how to do my specific use case.

An M:N table that links to an M:N table, applying a filter on all 3. For example:

A user has many projects, which has many tasks. When retrieving a user and doing an eager load on both project and tasks, I would expect the query to apply the ON query correctly (i.e. ON task_id = task.id AND project_id = project.id AND user_id = user.id)

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

I feel this is a common scenario and having a similar example could prove useful (apologies if there is one somewhere and I missed it). A section on having multi-associations somewhere.

Additional context

I have created a repl.it here to demonstrate my problem.

Issue Template Checklist

Is this issue dialect-specific?

• No. This issue is relevant to Sequelize as a whole.
• Yes. This issue only applies to the following dialect(s): XXX, YYY, ZZZ
• I don't know.

Would you be willing to resolve this issue by submitting a Pull Request?

• Yes, I have the time and I know how to start.
• Yes, I have the time but I don't know how to start, I would need guidance.
• No, I don't have the time, although I believe I could do it if I had the time...
• No, I don't have the time and I wouldn't even know how to start.

Start with the linked repl.it reproduction and the issue's description of nested many-to-many eager loading. Determine the expected behavior and document a comparable three-association example, including how the filters should be applied; done means the scenario and its limitations are clear in the Sequelize documentation.