[INTERNAL][FIX] sap.uxap.ObjectPageHeader: documentation updated
[INTERNAL][FIX] sap.uxap.ObjectPageHeader: documentation updated

Emphasizing that the control should be used in the ObjectPageLayout
and only this is supported.

Change-Id: I76c2d36bb14a4239e2975d386b41cc99bfe8fae5
BCP: 1780440710

cschuff/openui5,SAP/openui5,cschuff/openui5,SAP/openui5,SAP/openui5,SAP/openui5,cschuff/openui5