Deploy new tracker version

[josecelano]

• Graceful shutdown for event listeners torrust-tracker#1587
• Overhaul stats: Refactor AggregateValue in metrics package torrust-tracker#1585
• Overhaul stats: Remove internal non-labeled metrics  torrust-tracker#1584
• Add new "tracker demo" section to README torrust-tracker#1583

[josecelano]

Grafana dashboards before deployment:

[josecelano]

Grafana dashboard after deployment:

[josecelano]

There is an issue with the UDP Average Connect Time metric:

# HELP udp_tracker_server_performance_avg_processing_time_ns Average time to process a UDP connect request in nanoseconds
# TYPE udp_tracker_server_performance_avg_processing_time_ns gauge
udp_tracker_server_performance_avg_processing_time_ns{request_kind="connect",server_binding_address_ip_family="inet",server_binding_address_ip_type="plain",server_binding_ip="0.0.0.0",server_binding_port="6969",server_binding_protocol="udp"} 18446743710713731000
udp_tracker_server_performance_avg_processing_time_ns{request_kind="scrape",server_binding_address_ip_family="inet",server_binding_address_ip_type="plain",server_binding_ip="0.0.0.0",server_binding_port="6969",server_binding_protocol="udp"} 40927.05282530009
udp_tracker_server_performance_avg_processing_time_ns{request_kind="announce",server_binding_address_ip_family="inet",server_binding_address_ip_type="plain",server_binding_ip="0.0.0.0",server_binding_port="6969",server_binding_protocol="udp"} 29331.002378199326
udp_tracker_server_performance_avg_processing_time_ns{request_kind="connect",server_binding_address_ip_family="inet",server_binding_address_ip_type="plain",server_binding_ip="0.0.0.0",server_binding_port="6868",server_binding_protocol="udp"} 18446743710604753000

I will open an issue on the tracker repo.