HIVE-29468: Standalone HMS REST Catalog Server: Migrate to Spring Boot

[difin]

What changes were proposed in this pull request?

The Standalone REST Catalog Server is reimplemented to use Spring Boot instead of plain Java:

• Server framework – Uses Spring Boot with an embedded Jetty server instead of raw servlet wiring.
• Health checks – Adds Actuator liveness and readiness probes; readiness verifies HMS connectivity via Thrift.
• Observability – Exposes Prometheus metrics for Kubernetes HPA and monitoring.
• Configuration – Keeps port and other settings in MetastoreConf but bridges them into Spring (e.g., via system properties) so Spring Boot uses the configured port.
• Graceful shutdown – Uses Spring Boot’s shutdown handling with a configurable timeout.
  Standalone packaging – Adds a spring-boot-maven-plugin “exec” JAR for running the server as a standalone process.

Why are the changes needed?

Spring Boot improves how the Standalone REST Catalog Server is run and operated:

• Kubernetes support – Liveness and readiness probes (/actuator/health/*) let Kubernetes reliably route traffic and restart unhealthy pods. Readiness includes an actual HMS connectivity check instead of a simple config check.
• Observability – Prometheus metrics enable HPA, dashboards, and alerting, which is standard for production deployments.
• Operational behavior – Graceful shutdown and a well-defined lifecycle reduce the chance of dropped requests during restarts.
• Maintainability – Spring Boot replaces custom servlet wiring and configuration, and aligns with common patterns for cloud-native Java services.

Does this PR introduce any user-facing change?

If the standalone REST Catalog server is deployed in Kubernetes:

• Liveness/readiness probes – Configure HTTP probes to use the new actuator endpoints:
  -- Liveness: httpGet: /actuator/health/liveness
  -- Readiness: httpGet: /actuator/health/readiness
• Metrics/HPA – Prometheus scraping or custom metrics use /actuator/prometheus.

How was this patch tested?

Integration tests in TestStandaloneRESTCatalogServer where updated to run the Spring Boot standalone HMS rest catalog server, verify liveness and readiness probes, Prometheus metrics.