rgw: Add coverity annotations to ignore warnings about 32 bit time

rgw: Add coverity annotations to ignore warnings about 32 bit time
There are two types of occurences of this warning:
1. Where time intervals are stored. These intervals are generally
   very small (like 30s for TOTP window duration), and are unlikely to
   overflow. These are marked as false positives.
2. Where time data is written to disk. Moving to 64 bit time would
   require significant work to ensure backwards compatibility. These
   shall be addressed via a separate PR. A bug addressing this has been
   opened at https://tracker.ceph.com/issues/61160

Signed-off-by: Vedansh Bhartia <vedanshbhartia@gmail.com>