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/scripts/reproduce-starter-aop-break.sh

@@ -0,0 +1,8 @@
+#!/usr/bin/env bash
+# Reproduces, and captures, the real build error from adding spring-boot-starter-aop
+# on Spring Boot 4.1 -- the dependency every pre-Boot-4 Resilience4j guide tells you to add.
+set -uo pipefail
+cd "$(dirname "$0")/../broken-example"
+mvn -B -q compile 2>&1 | grep -v '^Picked up\|^WARNING' > ../docs/output/00-starter-aop-build-error.txt
+echo "captured to docs/output/00-starter-aop-build-error.txt:"
+cat ../docs/output/00-starter-aop-build-error.txt