FINERACT-2746: migrate organisation tests to feign

[DeathGun44]

Description

Migrates five organisation and reference-data integration test classes from REST-assured onto the generated Feign client.

Class	Tests
OfficeIntegrationTest	3
HookIntegrationTest	2 (1 disabled, see gaps)
ExternalEventConfigurationIntegrationTest	2
RatesTest	1
ProductMixIntegrationTest	1

No production code is changed. Every file is under integration-tests/, so the OpenAPI spec is untouched and checkBreakingChanges cannot regress. The PR shares no file with any other in-flight migration branch and can be merged in any order relative to them.

Helpers

• HookHelper and RatesHelper are deleted; ProductMixHelper moves to client/feign/helpers/FeignProductMixHelper. None had a caller outside its own test.
• ExternalEventConfigurationHelper loses 788 lines - a hand-maintained catalogue of the 146 default event configurations plus two helpers, all three with no callers left. Its two live methods stay; three other tests still use them.
• OfficeHelper is untouched: 20 other tests still depend on it.
• FeignExternalEventHelper now delegates its two configuration toggles to FeignExternalEventConfigurationHelper, so one class owns that endpoint.

Notable changes beyond the transport swap

• The 146 expected defaults collapse from 788 lines of maps to a set of type names in ExternalEventConfigurationTestData. Keeping the catalogue duplicated is deliberate: adding or removing an event type should fail this test until the set is updated. (The previous list had drifted out of date against the Liquibase seed.)
• The external-event update test re-reads the configuration afterwards, rather than trusting only the echoed changes map.
• RatesTest additionally asserts the new rate appears in the listing, and checks the update's changes payload against both the requested percentage and the persisted one.
• FeignHookHelper locates the payload URL by field name instead of by list position - the server promises no order there, so config.get(1) happened to work rather than being correct. Field names come from the server's own HookApiConstants, so a rename breaks the build instead of the test.
• HookIntegrationTest deletes its hook in @AfterEach. Previously a failed assertion could leave an active OFFICE/CREATE webhook registered, making every later test that creates an office fire an outbound dispatch.

Known gaps left in place, each needing its own ticket

Pre-existing, called out rather than papered over:

1. CashierSummaryAndTransactionsTest is not migrated. It was in scope until the typed client turned out to be unable to create a teller. TellerApiResourceSwagger.PostTellersRequest.status is declared as TellerStatus, so the generated model sends "ACTIVE", but Teller.fromJson reads the field with integerValueOfParameterNamed("status") and expects an int. The server answers 400 error.msg.invalid.json.data. Correcting the DTO is production code and a breaking OpenAPI change, so it does not belong here.
2. ProductMixIntegrationTest can only assert that its two calls returned 200. The listing call does not send associations=productMixes, so it returns loan productsrather than product mixes; and with isProductMixTemplate=true the endpoint answers {"productOptions": [...]}, which the declared GetLoanProductsTemplateResponse has no field for, leaving every property null. Both are unchanged from before the migration and both need LoanProductsApiResourceSwagger changes to close.
3. shouldSendOfficeCreationNotification is @Disabled. It polls echo-webhook.herokuapp.com, offline since Heroku retired free dynos in 2022, so the loop always timed out and the test passed having asserted nothing - while still registering a hook and making the server attempt an outbound POST to a dead host on every CI run. The code is kept for whoever supplies a replacement echo endpoint.

Checklist

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