[HOTFIX] FINERACT-HOTFIX: Fix repayment template next unpaid installment amount

[shamir92]

Description

Updated the repayment transaction template query so it returns the next installment with an outstanding balance instead of always defaulting to the earliest installment.

This was needed because partially paid loans could produce an incorrect repayment template amount when the first matching installment was already fully satisfied. The change reuses the existing due amount expressions in the query ordering, and adds an integration test to verify the repayment template now returns the next unpaid installment amount.

Checklist

Please make sure these boxes are checked before submitting your pull request - thanks!

• Write the commit message as per our guidelines
• Acknowledge that we will not review PRs that are not passing the build ("green") - it is your responsibility to get a proposed PR to pass the build, not primarily the project's maintainers.
• Create/update unit or integration tests for verifying the changes made.
• Follow our coding conventions.
• Add required Swagger annotation and update API documentation at fineract-provider/src/main/resources/static/legacy-docs/apiLive.htm with details of any API changes
• This PR must not be a "code dump". Large changes can be made in a branch, with assistance. Ask for help on the developer mailing list.

Your assigned reviewer(s) will follow our guidelines for code reviews.

[San-43]

Please sign your commits as described in the CONTRIBUTING.md signing guide. Also, please use the required PR title format FINERACT-XXXX: Small descriptive sentence -- your pr should always reference a Jira ticket.