feat(server): update graceful shutdown behaviour

[franklinkim]

Adopt behaviour to follow kubernetes conditions. Will end up with sth like:

INFO    starting keel server
INFO    starting keel service    {"keel_service_type": "http", "keel_service_name": "http", "net_host_ip": "0.0.0.0", "net_host_port": "8080"}
INFO    starting keel service    {"keel_service_type": "http", "keel_service_name": "readme", "net_host_ip": "localhost", "net_host_port": "9001"}
INFO    starting keel service    {"keel_service_type": "http", "keel_service_name": "healthz", "net_host_ip": "0.0.0.0", "net_host_port": "9400"}
INFO    starting keel service    {"keel_service_type": "http", "keel_service_name": "pprof", "net_host_ip": "localhost", "net_host_port": "6060"}
INFO    starting keel service    {"keel_service_type": "http", "keel_service_name": "zap", "net_host_ip": "localhost", "net_host_port": "9100"}
INFO    starting keel service    {"keel_service_type": "http", "keel_service_name": "viper", "net_host_ip": "localhost", "net_host_port": "9300"}
INFO    starting keel service    {"keel_service_type": "http", "keel_service_name": "prometheus", "net_host_ip": "0.0.0.0", "net_host_port": "9200"}
INFO    keel graceful shutdown
INFO    keel graceful shutdown timeout    {"graceful_timeout": "30s", "shutdown_timeout": "30s"}
DEBUG    healthz probe failed    {"error_type": "*errors.errorString", "error_message": "server is shutting down", "http_target": "/healthz/readiness"}
DEBUG    healthz probe failed    {"error_type": "*errors.errorString", "error_message": "server is shutting down", "http_target": "/healthz/readiness"}
DEBUG    healthz probe failed    {"error_type": "*errors.errorString", "error_message": "server is shutting down", "http_target": "/healthz/readiness"}
INFO    keel graceful shutdown timeout complete
INFO    keel graceful shutdown closers
INFO    stopping keel service    {"keel_service_type": "http", "keel_service_name": "http"}
DEBUG    keel graceful shutdown closer closed    {"name": "*service.HTTP"}
INFO    stopping keel service    {"keel_service_type": "http", "keel_service_name": "zap"}
DEBUG    keel graceful shutdown closer closed    {"name": "*service.HTTP"}
INFO    stopping keel service    {"keel_service_type": "http", "keel_service_name": "readme"}
DEBUG    keel graceful shutdown closer closed    {"name": "*service.HTTP"}
INFO    stopping keel service    {"keel_service_type": "http", "keel_service_name": "viper"}
DEBUG    keel graceful shutdown closer closed    {"name": "*service.HTTP"}
INFO    stopping keel service    {"keel_service_type": "http", "keel_service_name": "prometheus"}
DEBUG    keel graceful shutdown closer closed    {"name": "*service.HTTP"}
INFO    stopping keel service    {"keel_service_type": "http", "keel_service_name": "healthz"}
DEBUG    keel graceful shutdown closer closed    {"name": "*service.HTTP"}
INFO    stopping keel service    {"keel_service_type": "http", "keel_service_name": "pprof"}
DEBUG    keel graceful shutdown closer closed    {"name": "*service.HTTP"}
DEBUG    keel graceful shutdown closer closed    {"name": "trace.noopTracerProvider"}
DEBUG    keel graceful shutdown closer closed    {"name": "nonrecording.noopMeterProvider"}
INFO    keel graceful shutdown complete
INFO    keel server stopped