Expose build numbers/commit sha information for both the angular UI and the dspace rest backend

[abollini]

In a CI environment or for heavily customized repository the "simple DSpace version" (#747 ) could be not enough, it should be possible to include the "build numbers" for both the frontend than the backend, these could ideally be the sha of the commit that was checked out during the build. It should be possible to configure the system to restrict these information to system administrator

[tdonohue]

Seems reasonable to me, I agree though that it either should be configurable or limited to Admins only. That said, it's lower priority than simply returning the DSpace version. Tentatively scheduling for 7.1

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