CLOSE - CSD02 - Fix grammar for "Constraints" on a Target node of a requirement (Chapter 11)

Section 11 of WD03, Rev05 has the following example which shows constraints on a requirement. The intent is to constrain the properties used for finding/matching the Target (Compute) node of a relationship. If we still want to allow this, we have no grammar for doing this and need one. Also, the grammar implied by the example perhaps is not sufficient to indicate that these constraints are on the properties of the Target node.

Here is the example as written:
node_templates:
mysql:
type: tosca.nodes.DBMS.MySQL
properties:

1. omitted here for sake of brevity
   requirements:

• host: tosca.nodes.Compute
  constraints:
• num_cpus: { in_range: [ 1, 4 ] }
• mem_size: { greater_or_equal: 2 }
• os_arch: x86_64
• os_type: linux
• os_distribution: ubuntu