feat: add Spring Boot Actuator health indicators for Mirror Node and Operator Balance

[Aamir377300]

This pr is solve #146

Description

This PR adds Spring Boot Actuator health indicators to improve the observability of Hiero-based Spring applications and introduces basic health indicators so applications can expose this information through the standard Actuator health endpoint.

While working with the Spring integration, I noticed there was no built-in way to monitor important runtime dependencies such as:

• Mirror Node connectivity
• operator account balance health

Changes Included

MirrorNodeHealthIndicator

Adds a lightweight connectivity check for the configured Mirror Node REST API to verify that it is reachable and responding correctly.

OperatorBalanceHealthIndicator

Checks the configured operator account balance and compares it against a configurable minimum threshold. If the balance becomes too low, the health details will expose a warning so teams can detect the issue earlier before transactions begin failing.

Configuration Support

Added configuration properties under:

spring.hiero.health.enabled=true
spring.hiero.health.min-balance-in-hbar=10

Auto Configuration

Introduced HieroHealthAutoConfiguration so the health indicators are automatically registered when Spring Boot Actuator is available on the classpath.

Dependency Update

Added spring-boot-starter-actuator as an optional dependency in the hiero-enterprise-spring module.

Verification

Verified successfully with:

./mvnw clean compile

Also verified the auto-configuration registration through HieroAutoConfiguration.

Edit:

Testing & Verification

To make sure the new health indicators behave correctly in different scenarios, I also added a dedicated unit test suite: HealthIndicatorTest.java

Test Coverage

The tests currently cover:

• successful health checks when the Mirror Node is reachable and the operator balance is healthy
• connectivity failure scenarios by mocking network/API exceptions
• low balance threshold handling
• failures while fetching account balance information

I also standardized the health detail response keys across both indicators during testing so the JSON output remains more consistent for monitoring tools and dashboards.

Verified successfully with:

./mvnw test -pl hiero-enterprise-spring -Dtest=HealthIndicatorTest

All tests are passing successfully.

Please review this pr @Ndacyayisenga-droid and I’d really appreciate feedback on the approach.