feat(content-explorer-modal-container): add noItemsRenderer prop

[psatala-box]

This PR adds noItemsRenderer prop to ContentExplorerModalContainer. When this prop is passed, it will be used instead of the default value. noItemsRenderer will only be rendered when items array is empty. This will be useful for specifying custom empty states.

This implements an idea suggested in #3241.

Here is an example:

To recreate this example, add the following line of code to examples/src/ContentExplorerMultiSelectModalContainerExamples.js:

noItemsRenderer={() => <p>This is a no items renderer</p>}