[server] Add missing indices for undo support (closes #3259691)
The tables used by the 'undo' feature were missing some indices, which
among other things triggered repeated sequential scans when deleting old
transactions.
usr/lib/PY_VERSION/*-packages/cubicweb/entities/
usr/lib/PY_VERSION/*-packages/cubicweb/ext/
usr/share/cubicweb/cubes/
usr/lib/PY_VERSION/*-packages/cubicweb/*.py