Adding keyspace_hits and keyspace_misses from Redis INFO stats

[allan-meng]

Looking to add keyspace_hits and keyspace_misses from Redis INFO stats.

Testing:

1. Started local kvrocks Docker container
   docker run -it -p 6666:6666 apache/kvrocks --bind 0.0.0.0
2. Started kvrocks_exporter
   ./kvrocks_exporter -kvrocks.addr kvrocks://localhost:6666
3. Set up redis-cli, added some keys, issued some GETs (some hits some misses)
   redis-cli -p 6666
4. Verified that keyspace_hits and keyspace_misses are reflected accurately in http://localhost:9121/metrics

# HELP kvrocks_keyspace_hits keyspace_hits metric
# TYPE kvrocks_keyspace_hits gauge
kvrocks_keyspace_hits 9
# HELP kvrocks_keyspace_misses keyspace_misses metric
# TYPE kvrocks_keyspace_misses gauge
kvrocks_keyspace_misses 3

[allan-meng]

@git-hulk Gentle nudge, just wanted to add some additional Redis INFO metrics.

[git-hulk]

@allan-meng Thank you!

[allan-meng]

@git-hulk Thank you for approving and merging this! I know it is a small change, but would it be possible to cut a minor release?

[git-hulk]

@allan-meng Sure, v1.0.5 is ready to use now. Thanks for your contribution again.

[allan-meng]

Thank you!!!