Upgrade xamarin project to MAUI/ Add push notification support for MAUI

[sacOO7]

• According to https://learn.microsoft.com/en-us/dotnet/maui/migration/?view=net-maui-8.0, xamarin support will end on may 1 2024, so there is detailed documentation provided to migrate the project.
• We already support MAUI for ably-dotnet, so just need to add push-notification support for MAUI.
• Also need to fix the xamarin build as a part of the issue.

┆Issue is synchronized with this Jira Task by Unito

[RsZoli]

@sacOO7 Any word on this? It would be much appreciated!

Thank you!

[sacOO7]

@RsZoli We are planning to address this issue sometime in the near future.