[DSpace 7 Upgrade] Reimplement Metadata Tree Browser Aspect

[jsavell]

Blocked by Add tamu theme shared component for collapsing sub communities and collections at the community collection views#14

https://github.com/TAMULib/DSpace/blob/tamu-dspace-6.3/dspace/config/xmlui.xconf#L90

https://github.com/TAMULib/DSpace/blob/tamu-dspace-6.3/dspace/modules/xmlui/src/main/resources/aspects/MetadataTreeBrowser/sitemap.xmap

https://github.com/TAMULib/DSpace/blob/tamu-dspace-6.3/dspace/modules/xmlui/src/main/java/edu/tamu/metadatatreebrowser/BrowseOverview.java
https://github.com/TAMULib/DSpace/blob/tamu-dspace-6.3/dspace/modules/xmlui/src/main/java/edu/tamu/metadatatreebrowser/BrowseNode.java

[Dbreck-TAMU]

XMLUI was removed in Dspace 7. Want to maintain feature parity.

[wwelling]

If we require the matching feature as OAKTrust we may need to either transfer this issue to DSpace or create an additional DSpace issue to modify or add an additional endpoint.