Add resilience4j-circuit-breaker: Resilience4j 2.4.0 vs Spring Framework 7 core, on Boot 4.1

Companion module for the rewritten post 'Resilience4j Circuit Breaker in Spring Boot 4.1:
What It's Still For', reworked around Framework 7 now shipping @Retryable/@ConcurrencyLimit
in core. Covers what's still Resilience4j's job (circuit breaker, rate limiter, bulkhead's
bounded wait, fallback methods, Actuator/Micrometer metrics), the off-by-one between
maxAttempts and maxRetries, and two Boot-4.1 build breaks: spring-boot-starter-aop no longer
exists (renamed to spring-boot-starter-aspectj, proven with Maven Central metadata and the
renamed starter's own POM -- see resilience/docs/08-starter-aop-renamed-to-starter-aspectj.md
in this same repo), and the resulting fix uses that renamed starter directly rather than
assembling spring-aop + aspectjweaver by hand. Kept as its own module rather than a new
top-level repository, alongside the existing resilience/ module for the sibling Framework-7
post.

resilience4j-circuit-breaker/src/main/resources/application.yml

@@ -0,0 +1,48 @@
+spring:
+  application:
+    name: resilience-boot4-demo
+
+server:
+  port: 8080
+
+management:
+  endpoints:
+    web:
+      exposure:
+        include: health,metrics,circuitbreakers,circuitbreakerevents
+  endpoint:
+    health:
+      show-details: always
+  health:
+    circuitbreakers:
+      enabled: true
+
+resilience4j:
+  circuitbreaker:
+    instances:
+      paymentService:
+        slidingWindowType: COUNT_BASED
+        slidingWindowSize: 10
+        minimumNumberOfCalls: 5
+        failureRateThreshold: 50
+        waitDurationInOpenState: 2s
+        permittedNumberOfCallsInHalfOpenState: 2
+        automaticTransitionFromOpenToHalfOpenEnabled: true
+        recordExceptions:
+          - com.ankurm.resilience.FlakyDownstream$DownstreamUnavailableException
+  bulkhead:
+    instances:
+      slowOp:
+        maxConcurrentCalls: 2
+        maxWaitDuration: 100ms
+  retry:
+    instances:
+      inventoryService:
+        maxAttempts: 3
+        waitDuration: 200ms
+        enableExponentialBackoff: true
+        exponentialBackoffMultiplier: 2
+
+logging:
+  level:
+    com.ankurm.resilience: INFO