Make it vendor agnostic in the configurations and environment variables

[pragmaticivan]

Is your feature request related to a problem? Please describe.
This project is really awesome and might be worth making it vendor-agnostic with optional authentication and support for sending data to otel collector.

Describe the solution you'd like
Add a few new configs:

• AuthEnabled bool
• AuthAccessTokenHeader string
• Default SPAN_ENDPOINT to otel collector (localhost)
• Derive ACCESS_TOKEN env var from config name.

Additional context
The usage for other vendors is pretty similar but this lib makes it way less complicated. Worth making it generic and perhaps donating that to cncf org one day?

[pragmaticivan]

I have a working version of that change:

type Config struct {
	SpanExporterEndpoint           string            `env:"OTEL_EXPORTER_OTLP_SPAN_ENDPOINT,default=0.0.0.0:4317"`
	SpanExporterEndpointInsecure   bool              `env:"OTEL_EXPORTER_OTLP_SPAN_INSECURE,default=false"`
	ServiceName                    string            `env:"SERVICE_NAME"`
	ServiceVersion                 string            `env:"SERVICE_VERSION,default=unknown"`
	Headers                        map[string]string `env:"OTEL_EXPORTER_OTLP_HEADERS"`
	MetricExporterEndpoint         string            `env:"OTEL_EXPORTER_OTLP_METRIC_ENDPOINT,default=0.0.0.0:4317"`
	MetricExporterEndpointInsecure bool              `env:"OTEL_EXPORTER_OTLP_METRIC_INSECURE,default=false"`
	MetricsEnabled                 bool              `env:"METRICS_ENABLED,default=true"`
	LogLevel                       string            `env:"OTEL_LOG_LEVEL,default=info"`
	Propagators                    []string          `env:"OTEL_PROPAGATORS,default=b3"`
	MetricReportingPeriod          string            `env:"OTEL_EXPORTER_OTLP_METRIC_PERIOD,default=30s"`
	AuthEnabled                    bool              `env:"AUTH_ENABLED,default=true"`
	AuthAccessTokenHeader          string            `env:"AUTH_ACCESS_TOKEN_HEADER,default=api-key"`
	ResourceAttributes             map[string]string
	Resource                       *resource.Resource
	logger                         Logger
	errorHandler                   otel.ErrorHandler
}

Usage with another vendor:

otelLauncher := otel.ConfigureOpentelemetry(
		otel.WithAuthAccessTokenHeader("api-key"),
		otel.WithServiceName("app-name"),
		otel.WithMetricExporterEndpoint("otlp.nr-data.net:4317"),
		otel.WithSpanExporterEndpoint("otlp.nr-data.net:4317"),
		otel.WithAccessToken("my-token"),
		otel.WithMetricsEnabled(true),
		otel.WithMetricReportingPeriod(time.Second*5)
	)

It could still default to light step *_ENDPOINT and perhaps lightstep-access-token in the token header