Fineract 2316 localize interest rate chart validation

[sidshas03]

Summary
This PR completes the i18n work for InterestRateChart slab validation and gets CI to green. Hard-coded/concatenated messages are replaced with message codes + arguments, message bundles are updated, focused tests cover overlap and gap scenarios, and spotless/checkstyle/spotbugs/tests pass locally.
Supersedes #4793 (credit to the original author and discussion).

What changed (final approach adopted)

• Domain stays Spring-free; standard validator pattern used

  // InterestRateChart.java
  DataValidatorBuilder v = new DataValidatorBuilder(errors)
      .resource("savings.interestRateChart")
      .parameter("slabs");
  v.failWithCode("overlap", slabContext, nextSlabContext);
  v.failWithCode("gap",     slabContext, nextSlabContext);

  Resolves to clean codes:

  • validation.msg.savings.interestRateChart.slabs.overlap
  • validation.msg.savings.interestRateChart.slabs.gap

• Message bundles (added/updated in fineract-provider/src/main/resources/messages.properties)

  validation.msg.savings.interestRateChart.slabs.overlap=There is an overlap between slabs {0} and {1}.
  validation.msg.savings.interestRateChart.slabs.gap=There is a gap between slabs {0} and {1}.
  

• Tests
  Added/updated unit tests to trigger overlap/gap and assert the exact codes (and arguments where exposed).

• CI
  Ran spotless, checkstyle, spotbugs, and tests locally — all green.

Alternatives evaluated and not taken (with reasons)

• Injecting MessageSource / LocaleContextHolder into domain/assemblers — rejected to keep the domain layer clean; Fineract typically passes codes + args and resolves messages later.
• Custom InterestRateChartDataValidatorBuilder subclass — rejected to avoid expanding API surface; standard builder suffices.
• Using full i18n keys while the builder had resource()/parameter() set — led to double-prefixed codes (e.g., validation.msg.interestRateChart.validation.msg.savings…).
• Using failWithCodeNoParameterAddedToErrorCode on a builder with context — could still introduce unwanted prefixes or null segments based on builder state.
• Direct ApiParameterError.parameterError(...) — functional but bypasses the usual validator aggregation flow; reverted for consistency.

Scope (files of interest)

• fineract-savings/src/main/java/.../InterestRateChart.java
• fineract-provider/src/main/resources/messages.properties (and optional locale bundles)
• fineract-savings/src/test/java/.../InterestRateChartValidationTest.java

Compatibility / API notes

• No REST schema changes.
• globalisationMessageCode for these validations now follows the standard validation.msg.savings.interestRateChart.* pattern.

How to verify

1. Build & checks:

   ./gradlew spotlessApply checkstyleMain checkstyleTest spotbugsMain spotbugsTest test

2. Confirm no hard-coded “overlap/gap” texts remain in InterestRateChart.java.

3. Run the updated tests; assertions should pass for the two codes above.

Housekeeping

• JIRA: defaults to FINERACT-2316; happy to switch to FINERACT-2181 if that is the intended ticket.
• Supersedes FINERACT-2181: Improve validation error messages for interest rate chart slabs in FD and RD products #4793; original author credited.

@bharathcgowda - following up from #4793.
I’ve opened this PR to localise the InterestRateChart slab validation using the minimal approach we discussed. Thank you so much for allowing me to work on it. Please kindly review and let me know.

[adamsaghy]

* What went wrong:
Execution failed for task ':rat'.

> A failure occurred while executing org.nosphere.apache.rat.RatWork
   > Apache Rat audit failure - 2 unapproved licenses
     	See file:///home/runner/work/fineract/fineract/build/reports/rat/index.html

[bharathcgowda]

@sidshas03 one check is failing, could you please check?

[bharathcgowda]

@adamsaghy could you please help in review of this PR?

[IOhacker]

@sidshas03 are you still working on this PR?

[adamsaghy]

@sidshas03 Please rebase this PR with latest develop branch!