[StorageV2] Implement GC
Summary:
Here are some numbers from the benchmark:
```
(TOOLCHAIN) mtomic@poso:~/memgraph/build_release$ tests/benchmark/storage_v2_gc --num-threads 8
Config: NoGc, Time: 25.9836
Config: OnFinishGc, Time: 49.012
Config: 100msPeriodicGc, Time: 45.9856
Config: 1000msPeriodicGc, Time: 40.3094
```
```
(TOOLCHAIN) mtomic@poso:~/memgraph/build_release$ tests/benchmark/storage_v2_gc --num-threads 7
Config: NoGc, Time: 20.4256
Config: OnFinishGc, Time: 39.6669
Config: 100msPeriodicGc, Time: 30.7956
Config: 1000msPeriodicGc, Time: 35.128
```
It is not that bad if there is a core dedicated to doing garbage collection.
Reviewers: mferencevic, teon.banek
Reviewed By: mferencevic, teon.banek
Subscribers: pullbot
Differential Revision: https://phabricator.memgraph.io/D2168
8414479abe