Improve sonar ratings.

[mshima]

Overview of the feature request

We can improve sonar ratings.
In recent PRs:

• coverage has increase from 84% to 87%
• duplications has decrease from 2,5% to 1,8%
• issues has increased from 66 to 67

Actions:

• reduce issues by reworking the resource IT.
• reduce issued by implementing the mapper test.

Motivation for or Use Case

Related issues or PR

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[mshima]

I've opened #25153 to discuss 6 sonar issues.

[mshima]

Linked PRs fixed ~45 issues. Will be at 20 with last PR, not every issue was fixed by linked PRs.
Increased coverage by ~4,4%. It's at 91,7%, like as issues, not every gain was done by linked PRs.

We have 6 issues about QueryService, 6 issues about patch implementation #25153, 3 issues about CacheConfiguration file and 5 individual issues.

Suggested fixes:

• QueryService: Add a Specification Builder at jhipster-framework to simplify the application side.
• CacheConfiguration: ignore at sonar.properties or use metamodel for jpa.
• LiquibaseConfig: add a JHipsterProperty for async disabling
• Commented codes: Move to the generator's README.md and add a link to it.