Set CacheDirectoryPath automatically for Android apps

For MAUI we set a default value for the `CacheDirectoryPath` when initialising the SDK:
[https://github.com/getsentry/sentry-dotnet/blob/b42aa0160c614a6444ed18d6d7f325e7ab42ad3d/src/Sentry.Maui/SentryMauiOptions.cs#L24-L26]()

However we don't do this out of the box for native Android/iOS applications.

For Android, at least, this looks pretty straight forward. This is how it's done in MAUI (and we could just do the same in Sentry):
[https://github.com/dotnet/maui/blob/a6bc8521b6807900af876a207ed7717bd3bb3413/src/Essentials/src/FileSystem/FileSystem.android.cs#L11-L12]()