[Backport 15.2/15.3] Cross project copying of a document in channel manager does not update the sitemap in the target project

The problem is cache related.

The is a cache of a XPageSiteMapTreeItem composite which is a tree of all XPage documents, represented in a URL space tree

This cache has as cache-key a 'siteMapConfigurationIdentity' which is an identity object representing the SiteMap of the channel, which can be the siteMapConfigurationIdentity for 'core' or for a branch

When a new document gets added, the cache for all branches need to invalidate, however, only the cache for the currently opened branch in the Channel Mgr was invalidated. This is a problem as adding a document by copying the document to another branch would only invalidate the cache of the current branch and not the target branch (project)