[REFACTOR] Centralize custom health indicators under HealthModule

[aniebietafia]

Problem

Custom Actuator health indicators live inside their respective feature packages:

• brokers/kafka/health/KafkaHealthIndicator.java
• googlevision/health/GoogleVisionHealthIndicator.java

This scatters monitoring logic across different packages.

Proposed Solution

Consolidate all custom health indicators under a single package com.xtraction.api.shared.health under shared/.

User Stories

• As an SRE, I want monitoring and health check logic located in a single package namespace.

Acceptance Criteria

• Custom health indicator classes are relocated.
• The /actuator/health endpoint correctly aggregates and displays health check results.

Tasks

• Relocate health indicator classes.
• Update import statements.
• Query the Actuator health endpoint to verify integration.