FINERACT-2454: Migrate InstanceModeIntegrationTest from RestAssured to fineract-client-feign

[Dpk376]

What this PR does

Migrates InstanceModeIntegrationTest from the deprecated RestAssured-based
helpers to the typed fineract-client-feign client, as part of FINERACT-2454.

Changes

• SchedulerJobHelper: Added no-arg constructor; replaced getSchedulerJobIdByShortName
  and runSchedulerJob with feign-based implementations using FineractClientHelper
• InstanceModeIntegrationTest: Removed all RestAssured boilerplate (requestSpec,
  responseSpec, Utils.initializeRESTAssured()); migrated ClientHelper.createClient
  and schedulerJobHelper.runSchedulerJob calls to feign; error cases now use
  assertThrows(CallFailedRuntimeException.class, ...)

Checklist

• ./gradlew spotlessApply passed
• ./gradlew :integration-tests:compileTestJava passed
• No new RestAssured dependencies introduced

closes #FINERACT-2454

gsoc-fineract-evidence

[DeathGun44]

@Dpk376 please make sure to sign your commits ,refer [‎CONTRIBUTING.md]. Also Fineract-2441 points to BI connector and demonstration ,please create a separate issue to properly track this via JIRA.

[Dpk376]

@Dpk376 please make sure to sign your commits ,refer [‎CONTRIBUTING.md]. Also Fineract-2441 points to BI connector and demonstration ,please create a separate issue to properly track this via JIRA.

Hi @DeathGun44 , thanks for the feedback!

Commit signatures: All commits are now GPG-signed and verified. You can see the "Verified" badge on each commit.
JIRA ticket: Agreed — I've updated the PR to reference FINERACT-2454 ("fineract-client-feign usage for integration tests"), which is the correct ticket tracking this migration work. FINERACT-2441 has been removed from all commit messages and the PR title.
Let me know if there's anything else to address!