[FEATURE] Add structured JSON logging with correlation IDs for TransactionMs

[abengl]

Description
Replace default Spring Boot logging with structured JSON output and propagate a correlation ID through the full request chain so a single transfer can be traced across TransactionMs, AccountMs, and CustomerMs in log output.

Tasks

• Add logback-spring.xml to each microservice (TransactionMs, AccountMs, CustomerMs) configured to output structured JSON using logstash-logback-encoder
• Add a CorrelationIdFilter (WebFilter for WebFlux, OncePerRequestFilter for MVC) that reads X-Correlation-ID from the incoming request header or generates a UUID if absent
• Propagate the correlation ID to MDC so it appears in every log line for that request
• For outgoing WebClient calls (TransactionMs → AccountMs, CustomerMs → AccountMs), forward the X-Correlation-ID header in the request
• Replace all System.out.println or unstructured log calls with SLF4J structured log statements with meaningful context fields (accountId, customerId, transactionId where relevant)
• Validate that a single POST /api/v1/transactions/transfer produces log lines in TransactionMs and AccountMs sharing the same correlationId

Acceptance Criteria

• All log output is valid JSON in the microservice
• A transfer request produces log entries in TransactionMs and AccountMs with the same correlationId value
• If the caller provides X-Correlation-ID: abc123, that value appears in all downstream log lines
• If no header is provided, a UUID is generated and propagated
• Log lines include at minimum: timestamp, level, service, correlationId, message