修改gdb cache的key为gcache:md5(sql)方式

[larryclean]

目前写入缓存的key，是用sql，我认为这个方式不太简洁。

[codecov-commenter]

Codecov Report

Merging #1555 (2e76268) into master (6232c87) will not change coverage.
The diff coverage is 0.00%.

@@           Coverage Diff           @@
##           master    #1555   +/-   ##
=======================================
  Coverage   69.79%   69.79%           
=======================================
  Files         438      438           
  Lines       42421    42421           
=======================================
  Hits        29606    29606           
  Misses      10919    10919           
  Partials     1896     1896           

Flag	Coverage Δ
go-1.15	69.73% <0.00%> (+<0.01%)	⬆️
go-1.16	69.76% <0.00%> (+0.03%)	⬆️
go-1.17	69.72% <0.00%> (-0.05%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
database/gdb/gdb_model_select.go	71.89% <0.00%> (ø)
container/gtree/gtree_avltree.go	97.21% <0.00%> (-0.60%)	⬇️
os/gmutex/gmutex.go	97.36% <0.00%> (+2.63%)	⬆️

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