[type: feature] Support isBlank

[kerwin612]

Added BlankPredicateJudge class to support isBlank predicate

Make sure that:

• You have read the contribution guidelines.
• You submit test cases (unit or integration tests) that back your changes.
• Your local test passed ./mvnw clean install -Dmaven.javadoc.skip=true.

[kerwin612]

Can anyone respond to this PR? I created it in version 2.6.0, but now it's 2.6.1. 😂

[codecov-commenter]

Codecov Report

Merging #4983 (c45df1f) into master (184e4ba) will increase coverage by 0.02%.
Report is 1 commits behind head on master.
The diff coverage is 88.88%.

@@             Coverage Diff              @@
##             master    #4983      +/-   ##
============================================
+ Coverage     64.19%   64.21%   +0.02%     
- Complexity     8568     8574       +6     
============================================
  Files          1208     1209       +1     
  Lines         35900    35905       +5     
  Branches       3218     3219       +1     
============================================
+ Hits          23046    23058      +12     
+ Misses        10997    10988       -9     
- Partials       1857     1859       +2     

Files Changed	Coverage Δ
...pache/shenyu/admin/model/dto/RuleConditionDTO.java	81.48% <ø> (ø)
...g/apache/shenyu/admin/service/SelectorService.java	12.50% <ø> (+1.38%)	⬆️
...in/base/condition/judge/PredicateJudgeFactory.java	75.00% <80.00%> (-25.00%)	⬇️
...a/org/apache/shenyu/common/enums/OperatorEnum.java	95.83% <100.00%> (+0.18%)	⬆️
...ugin/base/condition/judge/BlankPredicateJudge.java	100.00% <100.00%> (ø)

... and 5 files with indirect coverage changes

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[li-keguo]

relevancy

apache/shenyu-dashboard#312

[moremind]

copy new sql named 2.6.1 from 2.6.0.sql, and add these fields to 2.6.1.sql and 2.6.0-to-2.6.1.sql

[moremind]

sorry, my means make a mistake, you must add it in init sql

[moremind]

sorry, my means make a mistake, you must add it in init sql

why need isBlank?

[kerwin612]

sorry, my means make a mistake, you must add it in init sql

why need isBlank?

With isBlank, I can do something when the parameter doesn't contain special field.

[moremind]

you need to add the field in opengauss database

[moremind]

you need to add the field in opengauss database

need 2.6.0-2.6.1-og.sql