dspace.cfg: Bring config inline with 4.1

Mostly just cleanups and new defaults, for example:

- The webui preview stuff is disabled by default, and we're not using it anyways, so we don't need our custom settings.
- webui.strengths.cache is enabled by default, so we don't need to enable it manully (and in the wrong place!)

Signed-off-by: Alan Orth <a.orth@cgiar.org>
dspace.cfg: Update consumers for 4.1

Discovery replaces search and browse in >= 4.0, and statistics is
for the Atmire stats.

Signed-off-by: Alan Orth <a.orth@cgiar.org>