[flutter_local_notifications] Add custom repeat interval - periodicallyShowWithDuration method

[mateuszluczak1996]

Add an option to set custom time for periodically showed notifications.

The problem that I have encountered on iOS devices is that repeating interval must be set to 60 seconds minimum, but I don't think that is the problem for real use case scenarios.

Sample usage:

    await flutterLocalNotificationsPlugin.periodicallyShowWithDuration(
      1,
      'repeating period title',
      'repeating period body',
      const Duration(minutes: 5),
      androidScheduleMode: AndroidScheduleMode.exactAllowWhileIdle,
    );

[MaikuB]

Thanks for the PR. Will need time to give this one a good review compared to some other ones

[MaikuB]

Thanks. Got to test it out and works well. Besides the comment on the PR, do you think you'd be able to look at the following

• addressing the linter issues picked up by Dart analyzer
• I ran into the limitation you mentioned with Apple's APIs when the duration needs to be a minute. Rather than letting it run into a native exception that may not bubble up to be caught on the Dart side, could validation be added to ensure the duration is at least a minute on all the platform-specific implementations and throw an ArgumentError? This would allow checking the argument up-front. If you're not sure how to do it, it'd be similar to how the ID is validated to ensure it's within range where there's a validateId() call in the plugin

[MaikuB]

Could you remove androidAllowWhileIdle argument? This is a new method so doesn't have to follow what's been done before and odd to add a new method with a deprecation notice applied to it immediately