Upgrade to otel sdk v2

[wpessers]

Still work in progress. Most of it should be covered by this PR, but still doing some smoke-testing on my own lambdas

[serkan-ozal]

Is VERSION no longer exported?

[serkan-ozal]

Why we need exporter-zipkin dependency?

[serkan-ozal]

Why we need to have and support Zipkin exporter by default?

[serkan-ozal]

I think, instead of else if (process.env.OTEL_TRACES_EXPORTER), we can try to get exporters from env if no span processor is configured by the configureTracer function before.

Because, even though configureTracer function is specified, user might not have interest to configure span processor (left its configuration to the Lambda layer here), but configure other properties of the TracerConfig.

And also, I think, OTEL_TRACES_EXPORTER env var should override the exporters set by the configureTracer function (for example, user is playing with different exporters without need to change the code and redeploy by just setting the env var.)

Therefore, I think, the following logic might be better:

• In the getExportersFromEnv, if there is no OTEL_TRACES_EXPORTER env var, return empty array.
• In the getExportersFromEnv, if OTEL_TRACES_EXPORTER is specified as none, return null.
• And here:

// Try to get exporters from env var
const exporters = getExportersFromEnv();

if (!exporters) {
  // `null` exporters means tracing exporter is disabled, so skip trace provider initialization
  return;
}

// If there is specified `configureTracer` function by the user, use it to setup the config
if (typeof configureTracer === 'function') {
  config = configureTracer(config);
}

if (exporters.length) {
  // If there are exporters configured by env var, clear the ones configured before.
  // Because, the exporters configured by env var should override the ones configured by code. 
  config.spanProcessors = []; 
  exporters.map(exporter => {
    if (exporter instanceof ConsoleSpanExporter) {
      config.spanProcessors.push(new SimpleSpanProcessor(exporter));
    } else {
      config.spanProcessors.push(new BatchSpanProcessor(exporter));
    }
  });
}

config.spanProcessors = config.spanProcessors || [];

// If no exporter configured, use the default one
if (config.spanProcessors.length === 0) {
  // Default
  config.spanProcessors.push(
    new BatchSpanProcessor(new OTLPTraceExporter()),
  );
}

// Logging for debug
if (logLevel === DiagLogLevel.DEBUG) {
  config.spanProcessors.push(
    new SimpleSpanProcessor(new ConsoleSpanExporter()),
  );
}

const tracerProvider = new NodeTracerProvider(config);

...