Refactor Extensions code to check protocol efficiently

[NassimBtk]

The OpenTelemetry-specific code is not passed to the protocol extension. Currently, the OpenTelemetry code observes the metric's value in the agent before sending it to the OTLP receiver.

The code you suggested is already implemented in the agent through the ProtocolHealthCheckStrategy, which is triggered at each collect cycle, except for the metricshub.host.protocol.up collect.

// Call the extensions to check the protocol health
final List<IProtocolExtension> protocolExtensions = extensionManager.findProtocolCheckExtensions(telemetryManager);
protocolExtensions.forEach(protocolExtension -> protocolExtension.checkProtocol(telemetryManager));

Indeed, the ProtocolHealthCheckStrategy can be updated to collect the protocol point, this will avoid code duplication in each extension. Several information are required from the TelemetryManager: hostname, configuration, so this can be passed as method arguments.

// Call the extensions to check the protocol health
final List<IProtocolExtension> protocolExtensions = extensionManager.findProtocolCheckExtensions(telemetryManager);
protocolExtensions.forEach(protocolExtension -> { 

    new MetricFactory()
        .collectNumberMetric(
            telemetryManager.getEndpointHostMonitor(),
            "metricshub.host.up{protocol=\"" + protocolExtension.getIdentifier() + "\"}",
            protocolExtension.checkProtocol(telemetryManager) ? UP : DOWN,
            telemetryManager.getStrategyTime()
        );
});

This can be done in a separate issue as it is a refactoring task. Moreover, each extension needs to be updated ;). By the way good catch, thanks @bertysentry.

Originally posted by @NassimBtk in #201 (comment)