Add Support for Health Checks

It would be great if the elastic-ilm support custom health checks with remediation based on client_info.json.

Example client info:

# Example client info entry
# "custom_checks": {
# "0": {
# "check": "/bin/bash /opt/elastic_stack/scripts/verify_acuity_custom_service.sh",
# "remediate": "/bin/bash /opt/elastic_stack/scripts/restart_acuity_custom_service.sh",
# "schedule": "15",
# "remediation_retries": "3",
# }
# },

Schedule would be dynamically set per entry. Thoughts?

- [ ] Add support for health checks. Look for proper exit code
- [ ] Add support for remediation checks. Run if check fails to exit properly
- [ ] Add support for custom schedules per health check
- [ ] Add support for remediation retry so it doesn't keep trying to remediate indefinitely

Start by locating how client_info.json is read and where existing health checks or scheduled tasks are handled. Define the behavior for custom check exit codes, remediation commands, per-check schedules, and remediation_retries; done means all four client_info.json options work without indefinite retries.

Written by the indexing model from the issue text.