Support defining update_allowed in the property_schema

This has a couple of advantages:
- docs will be easier to generate
- everything property related is in one place
- it's a bit easier dealing with TemplateResources
- it will allow us to set update_allowed on nested schema

Change-Id: I5e59bc07e51fe4c5d58871cb2adcef7e16f9b2af
Partial-bug: #1240583
Merge "Support defining update_allowed in the property_schema"