Optimize check field json field

[BigChaoChao]

1. 审核参数"enable_blob_type"，添加包含JSON字段类型；
2. 当审核参数"enable_nullable=false"时，不强制text\blob\json必须有NOT NULL约束；
3. text/blob/json 字段禁止设置NOT NULL约束。

[codecov]

Codecov Report

Merging #22 into master will increase coverage by 0.0038%.
The diff coverage is 0%.

@@               Coverage Diff                @@
##             master        #22        +/-   ##
================================================
+ Coverage   62.9923%   62.9961%   +0.0038%     
================================================
  Files           371        371                
  Lines         77873      77873                
================================================
+ Hits          49054      49057         +3     
+ Misses        24626      24621         -5     
- Partials       4193       4195         +2

[hanchuanchuan]

thanks!