[FAB-8660] Operations and PeerSupport interfaces

This introduces an interface that represents the currently exported
functions of the peer. An instance of the interface is created during
package initialization which delegates to the existing functions.

- References to the peer functions in endorser.Support are replaced with a
  reference to the peer singleton.
- CreatePeerServer is renamed to the more idiomatic NewPeerServer as it
  is a constructor
- PeerSupportFactory is removed and an instance of PeerSupport is
  provided to endorser.SupportImpl and scc.ProviderFactory

Change-Id: I07ae90092be8349bed60686f7b04a5b9ab02382a
Signed-off-by: Matthew Sykes <sykesmat@us.ibm.com>