feat: Add optional Accept-Language header configuration

[subhankarmaiti]

Changes

This change introduces an optional configuration setting, acceptLanguage, allowing developers to specify preferred language tags (e.g., "en-US", "fr-CA,fr;q=0.9") during SDK initialization. When provided, the SDK will automatically include the Accept-Language HTTP header with the specified value in all outgoing API requests.

• Usage Summary:
  Developers can now optionally provide an acceptLanguage string when initializing the SDK either via the Auth0 class constructor or the Auth0Provider component prop.

  // Using Auth0 class
  const auth0 = new Auth0({
    domain: 'YOUR_AUTH0_DOMAIN',
    clientId: 'YOUR_AUTH0_CLIENT_ID',
    acceptLanguage: 'es-ES,es;q=0.9' // Example value
  });
  
  // Using Auth0Provider
  <Auth0Provider
    domain="YOUR_AUTH0_DOMAIN"
    clientId="YOUR_AUTH0_CLIENT_ID"
    acceptLanguage="de-DE" // Example value
  >
    <App />
  </Auth0Provider>

  If provided, the Accept-Language header will be automatically included in subsequent API calls made by the SDK. This feature is optional and backward compatible; existing initializations without acceptLanguage will continue to function as before. An example has been added to EXAMPLES.md.

Testing

• This change adds unit test coverage.
  • Unit tests were added in src/networking/__tests__/index.spec.js to verify the Client class behavior:
    • Ensures the Accept-Language header is not added when the acceptLanguage option is omitted during initialization.
    • Ensures the Accept-Language header is added with the correct value for GET, POST, and PATCH requests when the acceptLanguage option is provided.
    • Ensures the acceptLanguage option is correctly stored during client initialization.

Checklist

• I have read the Auth0 general contribution guidelines
• All existing and new tests complete without errors
• All active GitHub checks have passed

[subhankarmaiti]

closing as #1155 is going to solve the same issue