[FEATURE] Add Prometheus metrics and a Grafana dashboard for TransactionMs

[abengl]

Description
Expose Prometheus-compatible metrics from the banking microservices and build a single Grafana dashboard focused on the transfer pipeline health: request rates, error rates, and latency.

Tasks

• Add micrometer-registry-prometheus to TransactionMs, AccountMs, and CustomerMs
• Expose /actuator/prometheus in each service (already have Actuator — just needs the endpoint enabled in properties)
• Add Prometheus and Grafana as services in docker-compose.yml
• Configure Prometheus prometheus.yml to scrape all three microservices
• Build a Grafana dashboard with the following panels:
  • Transfer request rate (requests/sec on POST /api/v1/transactions/transfer)
  • Transfer error rate (4xx and 5xx responses)
  • p95 latency for the transfer endpoint
  • Active HTTP connections per service
• Export the dashboard as dashboard.json and include it in the repository under /grafana
• Add a custom Counter metric in TransactionMs for transactions.completed and transactions.failed using Micrometer API directly

Acceptance Criteria

• http://localhost:9090 (Prometheus) shows all three services as targets with state UP
• http://localhost:3000 (Grafana) loads the dashboard without manual configuration after docker-compose up
• The dashboard updates in real time when the Generator runs a generation batch
• transactions.completed and transactions.failed counters are visible in Prometheus and the Grafana dashboard
• No hardcoded Grafana credentials beyond the default admin/admin dev setup