[TASK] Re-implement update TER extension list task

The scheduler task to update the TER extension list on a regular basis
was removed with the implementation of the new extension manager.
The patch adds an updated version of it and takes care that
existing registered tasks of this type still work.

Change-Id: Ic770ed78f23413b589352c25998eaee7863ec64f
Resolves: #39915
Releases: 6.0
Reviewed-on: http://review.typo3.org/16168
Reviewed-by: Felix Kopp
Tested-by: Felix Kopp
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters
Reviewed-by: Anja Leichsenring
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn