15.0.0

• GA4 support.
• Updated Angular to v16 and dropped support for older versions.
• Dropped rxjs v6 support. Now only rxjs v7 is supported.
• NgxGoogleAnalyticsModule.forRoot() and NgxGoogleAnalyticsRouterModule.forRoot() were replaced by provideGoogleAnalytics() and provideGoogleAnalyticsRouter() to set up library's providers.
• All directives are now standalone and can be imported separately or used as hostDirectives in other directives.
• GoogleAnalyticsService methods now use options objects to specify additional arguments instead of a long list
  of arguments with some of the arguments undefined. Thanks, @Spejik, for the implementation.

Before:

this.gaService.pageView('/test', 'Test the Title', undefined, {
  user_id: 'my-user-id'
});

After:

this.gaService.pageView('/test', {
    title: 'Test the Title',
    options: {
        user_id: 'my-user-id'
    }
});