tools: ceph-objectstore-tool is able to trim pg log dups' entries.

tools: ceph-objectstore-tool is able to trim pg log dups' entries.

The main assumption is trimming just dups doesn't need any update
to the corresponding pg_info_t.

Testing:

1. cluster without the autoscaler
```
rzarz@ubulap:~/dev/ceph/build$ MON=1 MGR=1 OSD=3 MGR=1 MDS=0 ../src/vstart.sh -l -b -n -o "osd_pg_log_dups_tracked=3000000" -o "osd_pool_default_pg_autoscale_mode=off"
```

2. 8 PGs in the testing pool.
```
rzarz@ubulap:~/dev/ceph/build$ bin/ceph osd pool create test-pool 8 8
```

3. Provisioning dups with rados bench
```
bin/rados bench -p test-pool 300 write -b 4096  --no-cleanup
...
Total time run:         300.034
Total writes made:      103413
Write size:             4096
Object size:            4096
Bandwidth (MB/sec):     1.34637
Stddev Bandwidth:       0.589071
Max bandwidth (MB/sec): 2.4375
Min bandwidth (MB/sec): 0.902344
Average IOPS:           344
Stddev IOPS:            150.802
Max IOPS:               624
Min IOPS:               231
Average Latency(s):     0.0464151
Stddev Latency(s):      0.0183627
Max latency(s):         0.0928424
Min latency(s):         0.0131932
```

4. Killing osd.0
```
rzarz@ubulap:~/dev/ceph/build$ kill 2572129 # pid of osd.0
```

5. Listing PGs on osd.0 and calculating number of pg log's entries and
dups:

```
rzarz@ubulap:~/dev/ceph/build$ bin/ceph-objectstore-tool --data-path dev/osd0 --op list-pgs --pgid 2.c > osd0_pgs.txt
rzarz@ubulap:~/dev/ceph/build$ for pgid in `cat osd0_pgs.txt`; do echo $pgid; bin/ceph-objectstore-tool --data-path dev/osd0 --op log --pgid $pgid | jq '(.pg_log_t.log|length),(.pg_log_t.dups|length)'; done
2.7
10020
3100
2.6
10100
3000
2.3
10012
2800
2.1
10049
2900
2.2
10057
2700
2.0
10027
2900
2.5
10077
2700
2.4
10072
2900
1.0
97
0
```

6. Trimming dups
```
rzarz@ubulap:~/dev/ceph/build$ CEPH_ARGS="--osd_pg_log_dups_tracked 2500 --osd_pg_log_trim_max=100" bin/ceph-objectstore-tool --data-path dev/osd0 --op trim-pg-log-dups --pgid 2.7
max_dup_entries=2500 max_chunk_size=100
Removing keys dup_0000000020.00000000000000000001 - dup_0000000020.00000000000000000100
Removing keys dup_0000000020.00000000000000000101 - dup_0000000020.00000000000000000200
Removing keys dup_0000000020.00000000000000000201 - dup_0000000020.00000000000000000300
Removing keys dup_0000000020.00000000000000000301 - dup_0000000020.00000000000000000400
Removing keys dup_0000000020.00000000000000000401 - dup_0000000020.00000000000000000500
Removing keys dup_0000000020.00000000000000000501 - dup_0000000020.00000000000000000600
Finished trimming, now compacting...
Finished trimming pg log dups
```

7. Checking number of pg log's entries and dups
```
rzarz@ubulap:~/dev/ceph/build$ for pgid in `cat osd0_pgs.txt`; do echo $pgid; bin/ceph-objectstore-tool --data-path dev/osd0 --op log --pgid $pgid | jq '(.pg_log_t.log|length),(.pg_log_t.dups|length)'; done
2.7
10020
2500
2.6
10100
3000
2.3
10012
2800
2.1
10049
2900
2.2
10057
2700
2.0
10027
2900
2.5
10077
2700
2.4
10072
2900
1.0
97
0
```

Conflicts:
        src/tools/ceph_objectstore_tool.cc -- undetected conflict
        with d5445b8f113797718a0dbb05e884a6bffbfed76a. Fixed by
        adopting the patch no not require the `unique_ptr<T>::get()`.

Fixes: https://tracker.ceph.com/issues/53729
Signed-off-by: Radosław Zarzyński <rzarzyns@redhat.com>
(cherry picked from commit a2190f901abf2fed20c65e59f53b38c10545cb5a)