LPS-38130 Add constants to handle layout related import actions
LPS-38130 Use action attribute instead of the delete
LPS-38130 Add all the site layouts to the lar manifest but export only the selected ones
LPS-38130 Do not validate unselected layouts when import
LPS-38130 Do not use the staging group from import process because it doesn't work when remote staging or remote lar import
LPS-38130 Use all the source layout id's when determine missing layouts but import only the selected ones
LPS-38130 Add integration test