Add launch source for hearing device dialog logs

By knowing where the dialog is launched can help us better improve the
user flow.

Flag: EXEMPT simple log added
Bug: 354606934
Test: manually check on go/atomviewer
Test: atest HearingDevicesTileTest HearingDevicesDialogDelegateTest HearingDevicesDialogManagerTest
Change-Id: Id99af22024dca5ab93bcd07552d567cf4973cdb5