🗑️ Deprecate the BaseHealthIndicatorService in favor of the HealthChecker interface

[flovouin]

📝 Description of the PR

This follows the deprecation of HealthIndicator in @nestjs/terminus. There is no point to providing a base class (BaseHealthIndicatorService) anymore. Services should implement the newly defined HealthChecker interface (from this runtime), and can use/inject the HealthIndicatorService (from @nestjs/terminus) to create a HealthIndicatorResult.

📋 Check list

• 🧪 Unit tests have been written.
• 📝 Documentation has been updated.