crimson/osd/lsan_suppressions.cc: Add MallocExtension::Initialize()

crimson/osd/lsan_suppressions.cc: Add MallocExtension::Initialize()

In similarity to lsan.supp:
```
leak:^MallocExtension::Register
```

Shouls suppress this:
```
==2692420==ERROR: LeakSanitizer: detected memory leaks

Direct leak of 45 byte(s) in 1 object(s) allocated from:
    #0 0x5641d4ffaedd in operator new(unsigned long) (/home/jenkins-build/build/workspace/ceph-pull-requests/build/bin/unittest-object-data-handler+0x7c01edd) (BuildId: 7aeb00a388469f4de54fedaaceb47fc006ce2906)
..
    #7 0x7fb22a6426f0 in MallocExtension::Initialize() (/lib/x86_64-linux-gnu/libtcmalloc.so.4+0x2a6f0) (BuildId: eeef3d1257388a806e122398dbce3157ee568ef4)
```

Signed-off-by: Matan Breizman <mbreizma@redhat.com>