Support for OpenTelemetry metrics

Added

• Add OpenTelemetry metrics endpoint. The collector can now receive OpenTelemetry metrics exports n the 0.0.0.0:8099/v1/metrics endpoint. The following metric types are supported: Gauge, Sum and Histogram. Configure your OpenTelemetry SDK to export to this application to track OpenTelemetry metrics in AppSignal.

Changed

• Rename the 'port' config option to 'http_port'. This better describes which port the configuration option is for.
• Use default transmission interval when invalid transmission interval values are set.
• Retry binding HTTP port for 5 times if it's in use. This gives the collector a longer time to connect to the port if it becomes available within a 4 minute window.
• Show all config errors on collector start failure. This will help resolve all errors at once rather than fix one at a time.
• Show all errors on OpenTelemetry's export request's resource validation. When one or more resource attributes are missing from the export request's resources, all errors are listed.

Fixed

• Report metrics for not sampled traces when actions reached the sampling rate. Now metrics are reported for all traces.

This release can be installed through our collector packages and Docker image.