add config option for safe volume warning

Add boolean configuration option config_safe_media_disable_on_volume_up
to customize the behavior of safe volume warning dialog:
- When true the dialog can be dismissed with a single press on Vol+ key
(default AOSP behavior)
- When false it cannot.

Initially disabled for Vodaphone DE, UK, ES and IT.

Bug: 65155536
Bug: 111667485
Test: make
Change-Id: I538d91e570fc962c93264db000dfcfdce90da1f0