Bug 20443: Fix patron modification approval

Bug 20443: Fix patron modification approval

There was a mismatch between "value" and "attribute". Before this
patchset, "value" was sometimes used, but then it comes "attribute" to
match the DB column's name.
We must keep both here, when an upgrade is done we could have "value"
that is still in the borrower_modifications.extended_attributes JSON

Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>