Add documentation about `LaunchMode` on Android as it relates to multi window.

### Type of issue

Missing information

### Description

A number of users have ran into issues with scenarios related to multi-window behavior and how android handles activities.

We're going to add some better logging into MAUI itself and modify the templates
https://github.com/dotnet/maui/pull/21492

But, if users want multi window now on Android they'll need to understand the difference between various launchModes on android to fit their scenario.

LaunchModes are a pretty deep topic so we can just give a recommendation to delete the launchmode if they want multi window support but to read through https://developer.android.com/guide/topics/manifest/activity-element#lmode to fully understand how Android handles launchmodes.

It would also be useful to highlight that for single window scenarios users should wire into the `OnNewIntent` lifecycle if they want to process requests coming in to the existing activity.

### Page URL

https://learn.microsoft.com/en-us/dotnet/maui/fundamentals/windows?view=net-maui-8.0

### Content source URL

https://github.com/dotnet/docs-maui/blob/main/docs/fundamentals/windows.md

### Document Version Independent Id

c7dc34b7-8355-cff9-6754-c9fdefade29a

### Article author

@davidbritch

### Metadata

* ID: c7dc34b7-8355-cff9-6754-c9fdefade29a
* Service: **dotnet-mobile**
* Sub-service: **dotnet-maui**