[ LatestPosts ] Move the new multiple category selector to QueryControls

[draganescu]

Describe the bug
In #20781 we added a multiple select control to the LatestPosts block which allows filtering the posts by multiple categories.

However, the control is being used directly in the block instead of the reusable QueryControls component. Given that the block itself is to be refactored at some time in the future to use the new QueryBlock it is important that we keep the filtering together in a component so we can more easily migrate when the time comes.

Expected behavior
The new filter should be in the QueryControls component.

[draganescu]

Solved in #20832