Add local debug flag to make AODPromotedNotificationViewModel dump content

We don't want to dump this data in production builds, since it contains
notification text, which could include things like privafte
conversations, but sometimes I need to see what content is being fed to
the AOD RON Composable, so add a local debug flag that defaults to false
that will make FlowDumperImpl also dump the content model when dumping
the view model.

Bug: 369151941
Flag: com.android.systemui.aod_ui_rich_ongoing
Test: manual
Change-Id: I368ab47d326de52b78014590e53b90a2cf2ca57e