Bug 29540: Raise flagsrequired in modrequest

Bug 29540: Raise flagsrequired in modrequest

Test plan:
Try modrequest with a user having only 'catalogue' perms and the following URLs:
[1] /cgi-bin/koha/reserve/modrequest.pl?reserve_id=XX&CancelBorrowerNumber=XX&CancelItemnumber=XX&biblionumber=XX
    Fill the XXs with correct identifiers for some item level hold.
[2] /cgi-bin/koha/reserve/modrequest_suspendall.pl?suspend=1&suspend_until=2021-12-01&borrowernumber=XX
    Fill the XX with borrowernumber for borrower that has pending holds.
You should see: Error: You do not have permission to access this page.

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
[AMENDED] More consensus for using reserveforothers than circulate_remaining.

Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
(cherry picked from commit 15285ae209f5a98ab2e77c730b0b70ff0b29c283)
Signed-off-by: Victor Grousset/tuxayo <victor@tuxayo.net>