Entity Hub: Refactor get children to work with added entity types support

Is there an existing issue for this?

• I have searched the existing issues.

Please describe the feature you have in mind and explain what the current shortcomings are?

Current implementation of childrens logic in EntityHub works only for folders and tasks, that does not include products and versions.

How would you imagine the implementation of the feature?

First of all it should be possible to get children of products.

Second issue is that it should be possible to get products as children of folders, but becuase the current logic counts only with folders it is not that easy. When currently available methods are called we should also fetch products with other folders and tasks. But we should add more targetted methods to get only folders, or only products or only tasks, and fetch them and cache their entities respectivelly, so when folder already has known folder entities, but get_children is called we should also look for tasks and products.

Another question is if tasks should option to have version entities as children, because the connection is there we might add it.

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Describe alternatives you've considered:

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Additional context:

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