Add file processing status to importer health checks

[steven-sheehy]

Problem
If the importer encounters a deadlock or some other scenario that causes it to stop processing new files, it is unable to recover by itself.

Solution

• Implement a Spring Boot HealthIndicator that checks if new stream files are processing. It can simply inject the MeterRegistry and ensure the counts for each of the stream types is increasing at some reasonable rate.
• Add new health check to management.endpoint.health.group.liveness.include
• Add new health check to management.endpoint.health.group.readiness.include

Note that liveness probes are disabled by default for importer since netty doesn't start until after Flyway finishes migrating. We will separately need to solve this issue.

Alternatives
Only use in readiness probe and allow another importer pod take over once leadership election race conditions are handled.

Additional Context