[Admin UI] Update Subject Request status filter to be a multiselect dropdown

[adriaaaa]

Currently the SR status filter is a single select. We should update this to be a multiselect so that users can filter for multiple SR statuses at once.
BE ticket to support this - #660
Mockup

[chriscalhoun1974]

@adriaaaa @seanpreston After discussing the multi-select design for the SR status dropdown with Adria, the SR dropdown will display multiple selected items in a comma delimited list. In the event the comma delimited list does not fit the width of the dropdown container, an ellipsis will be appended to the right of the text. If the user is to hover over the dropdown, a tooltip will be displayed rendering the comma delimited list in its entirety.

[chriscalhoun1974]

@adriaaaa @seanpreston I have updated the PR. BE and FE are working together as designed. Its ready for Code Review. However, can someone give me any guidance as to updating any appropriate Admin UI documentation if needed as part of the PR? Thank you.