Maintenance: Resolve initial batch of Java compilation warnings in fineract-provider

[pranjal-singla-15]

This PR addresses the general goal of improving codebase safety and maintainability by resolving compilation warnings, as suggested in the community's beginner-friendly task list.

Resolve warnings:

1. Warning: Deprecated setCellType in Apache POI

File: FixedDepositTransactionWorkbookPopulator.java
File Path: fineract-provider/src/main/java/org/apache/fineract/infrastructure/bulkimport/populator/fixeddeposits/FixedDepositTransactionWorkbookPopulator.java
Line Number: 108
Warning Type
Deprecation Warning - [deprecation]

2. Warning: Deprecated setCellType in Apache POI

File: RecurringDepositTransactionWorkbookPopulator.java
Deprecation Warning - [deprecation] setCellType(CellType) in Cell has been deprecated

3.Warning: Depracated setCellType in Apache POI

File:
SavingsTransactionsWorkbookPopulator.java
File Path:
fineract-provider/src/main/java/org/apache/fineract/infrastructure/bulkimport/populator/savings/SavingsTransactionsWorkbookPopulator.java 

4.Warning: Deprecation Fix - ExecuteReportMailingJobsTasklet
File Name: ExecuteReportMailingJobsTasklet.java
File Path: fineract-provider/src/main/java/org/apache/fineract/infrastructure/campaigns/jobs/executereportmailingjobs/ExecuteReportMailingJobsTasklet.java
Line Number: 101
Previous code: StringUtils.containsIgnoreCase(key, "date")
Proposed fix: key != null && key.toLowerCase().contains("date")

5.Warning: Deprecation Fix - ReportMailingJobEmailAttachmentFileFormat
File: ReportMailingJobEmailAttachmentFileFormat.java
File Path: fineract-provider/src/main/java/org/apache/fineract/infrastructure/reportmailingjob/data/ReportMailingJobEmailAttachmentFileFormat.java
Line no.: 53,55, 57
Proposed fix:
Replaced StringUtils with native Java String.equalsIgnoreCase().

6.Warning: [dep-ann] deprecated item is not annotated with @deprecated
File: CustomAuditingHandler.java
File path: fineract\fineract-provider\src\main\java\org\apache\fineract\infrastructure\core\auditing\CustomAuditingHandler.java
Line no.: 56
Proposed fix: Added @deprecated annotation to the deprecated constructor

[adamsaghy]

Please make sure to follow proper PR title and commit message convetions:
FINERACT-2421: Resolve initial batch of Java compilation warnings in fineract-provider

Please kindly follow the documentation to set up GPG signature for your github user.

FAILURE: Build completed with 2 failures.

1: Task failed with an exception.
-----------
* What went wrong:
Execution failed for task ':fineract-provider:licenseMain'.
> License violations were found: /home/runner/work/fineract/fineract/fineract-provider/src/main/java/org/apache/fineract/infrastructure/bulkimport/populator/fixeddeposits/FixedDepositTransactionWorkbookPopulator.java}

* Try:
> Run with --stacktrace option to get the stack trace.
> Run with --info or --debug option to get more log output.
> Get more help at https://help.gradle.org./
==============================================================================

2: Task failed with an exception.
-----------
* What went wrong:
Execution failed for task ':fineract-provider:checkstyleMain'.
> A failure occurred while executing org.gradle.api.plugins.quality.internal.CheckstyleAction
   > Checkstyle rule violations were found. See the report at: file:///home/runner/work/fineract/fineract/fineract-provider/build/reports/checkstyle/main.html
     Checkstyle files with violations: 1
     Checkstyle violations by severity: [error:1]

==============================================================================