Added filter bar into add issues modal

What does this MR do?

Adds the filter bar into the issue boards add issues modal window. This required a bit more tweaking of the filtered search code, it was previously only setup to allow 1 per page whereas on issue boards we need 2 on the page at the same time.

A 'container' class has been created with will return the current container for the filtered search bar. The container is updated to the modal window when it is opened & then set back to the document when it is closed. This is the quickest way to do this without re-factoring to the filtered search to not include static methods.

The only real difference between this bar & the bar on the issue boards is that the URL never updates, the filter is effectively lost when the modal is closed.

Screenshots (if relevant)