feat: modify the SDK initialization options to allow adding Exporter headers

[devlasbe]

Summary

modify the SDK initialization options to allow adding Exporter headers.

I added a header option to authenticate with a monitoring cloud system that follows the OpenTelemetry standard.

Test plan

After building the package, I added headers to the SDK initialization options in the example app and verified them in the Network tab of the web browser.

const sdk = openTelemetrySDK({
  // Use '10.0.2.2' instead of 'localhost' on Android emulators
  url: "http://localhost:4318",
  headers: {
    Authorization: "Test Access Token", // ADD
  },
  debug: true,
  name: "MyExampleApp",
  version: "1.0.0-alpha",
  environment: "development",
  features: {
    session: {
      getSessionId: () => "custom-session-id",
    },
  },
});

[devlasbe]

@adhorodyski review please