Rocksdb optimize option support config

[absolute8511]

support some configuration for rocksdb to optimize the write.

[codecov]

Codecov Report

Merging #43 into master will decrease coverage by 0.27%.
The diff coverage is 11.79%.

@@            Coverage Diff             @@
##           master      #43      +/-   ##
==========================================
- Coverage   44.64%   44.36%   -0.28%     
==========================================
  Files         149      149              
  Lines       21411    21571     +160     
==========================================
+ Hits         9559     9571      +12     
- Misses      10302    10436     +134     
- Partials     1550     1564      +14

Impacted Files	Coverage Δ
rockredis/t_hll.go	75.7% <ø> (-0.12%)	⬇️
node/config.go	100% <ø> (ø)	⬆️
node/state_machine.go	21.46% <0%> (ø)	⬆️
server/server.go	56.88% <0%> (-1.3%)	⬇️
node/kvstore.go	46.37% <100%> (+0.78%)	⬆️
node/node.go	32.33% <16.66%> (-0.33%)	⬇️
node/namespace.go	32.21% <3.84%> (-1.9%)	⬇️
server/httpapi.go	13.13% <4.54%> (-0.54%)	⬇️
node/raft.go	36.06% <50%> (-0.05%)	⬇️
rockredis/t_hash.go	60.24% <66.66%> (+0.16%)	⬆️
... and 5 more

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[absolute8511]

maybe partly solved #42