(KDropdownMenu): Allow KDropdownMenu to be used as an inline element

[habibayman]

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Target branch: develop

Current behavior

The default behavior is that all KDropDownMenus are block elements, with no 100% reliable way of using them as inline elements.

Desired behavior

I want to be able to use it as an inline element, using a custom prop perhaps.

Value add

This will be beneficial for the Learner Facing QTI Interactions project that is about to start.
Especially for the inline question interaction type.

Possible tradeoffs

We can rebuild it using native <Select/> component but honestly I don't think this is a good idea as we'll have to go through the process of implementing a lot of things that already exist here.

[habibayman]

No longer needed, after further research: I think Kselect is even a more worth candidate to use.