Add `immutable` property attribute

Currently resources support only in-place update or (default)
UpdateReplace. In order to support AWS "Updates are not supported"
feature, this new property attribute is added, with default value False.
It is going to be used for denying an UpdateReplace
behavior of the resource (similar to update_allowed currently).

Change-Id: Ie94241630d9595b58ff6b84bcb94459b0785fc03
Implements: blueprint implement-aws-updates-not-supported
Merge "Add `immutable` property attribute"