Factor workspaces support library out of workflow server.

services/workflow/setup.py

services/workflow/src/workflow/server.py

shared/workspaces/README.md

shared/workspaces/setup.py

shared/workspaces/src/workspaces/__init__.py

shared/workspaces/src/workspaces/_version.py

shared/workspaces/src/workspaces/interfaces.py

shared/workspaces/src/workspaces/schema.py

shared/workspaces/src/workspaces/services.py