Use configured JsonMapper bean when resolving JacksonJsonSerde

[adityaanikam]

Fixes gh-3231

What / why

SerdeResolverUtils.resolveForType() falls back to new JacksonJsonSerde<>(genericRawClazz) (the no-arg-mapper constructor) whenever no matching Serde bean and no valid fallback are found. This means any JsonMapper bean configured in the application context — for spring.jackson.* customization or otherwise — is never picked up for Serdes created through this path, even though JacksonJsonSerde has a (Class, JsonMapper) constructor that supports exactly this.

Fix

Look up a JsonMapper bean from the context (context.getBeanProvider(JsonMapper.class).getIfUnique()) and pass it into JacksonJsonSerde's constructor when exactly one unambiguous bean is present, falling back to today's no-arg behavior otherwise (zero or multiple candidates).

Testing

Added SerdeResolverUtilsTests.ResolveForType.NoMatchingSerdeBeans.WithJsonMapperBean, which registers a custom JsonMapper bean and verifies (via the JacksonJsonSerializer internal field) that the exact same instance is wired into the resolved Serde. Ran the full spring-cloud-stream-binder-kafka-streams test suite locally (122 tests, 0 failures, 0 errors) to confirm no regressions.