Add flag `enable_device_suggestions_preference` in the Media namespace.

Replace the flag `com.android.settings.flags.device_suggestions_preference`
with `com.android.media.flags.enable_device_suggestions_preference`.

Flag: com.android.media.flags.enable_device_suggestions_preference
Test: locally on a dev device
Bug: 415096359
Change-Id: Ief67a45065990fedd9f1f33fcc3b37d79f4d3efc