Refactor network component props to file for usnistgov#1913

As there will duplicate values when they really need to be identical and
the enum documentation strings were previously aligned, it is prudent to
refactor the reused enum values and doc strings using the shared entity
file pattern per other shared allowed-values enum sets in this model
definition and others.

src/metaschema/oscal_implementation-common_metaschema.xml

@@ -10,6 +10,7 @@
       <!ENTITY allowed-values-component_inventory-item_property-name SYSTEM "./shared-constraints/allowed-values-component_inventory-item_property-name.ent">
       <!ENTITY allowed-values-component_component_link-rel SYSTEM "./shared-constraints/allowed-values-component_component_link-rel.ent">
       <!ENTITY allowed-values-component-type SYSTEM "./shared-constraints/allowed-values-component-type.ent">
+      <!ENTITY allowed-values-property-name-networked-components SYSTEM "./shared-constraints/allowed-values-property-name-networked-components.ent">
 ]>
 <METASCHEMA xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns="http://csrc.nist.gov/ns/oscal/metaschema/1.0" xsi:schemaLocation="http://csrc.nist.gov/ns/oscal/metaschema/1.0 ../../build/metaschema-xslt/support/metaschema/schema/xml/metaschema.xsd" abstract="yes">
@@ -192,16 +193,10 @@
                         <enum value="isa-title">Title of the Interconnection Security Agreement (ISA).</enum>
                         <enum value="isa-date">Date of the Interconnection Security Agreement (ISA).</enum>
                         <enum value="isa-remote-system-name">The name of the remote interconnected system.</enum>
-                        <enum value="ipv4-address">The Internet Protocol Version 4 address is for an interconnection, service, or software component.</enum>
-                        <enum value="ipv6-address">The Internet Protocol Version 6 address is for an interconnection, service, or software component.</enum>
-                        <enum value="direction">The direction categorizes the network connectivity of an interconnection, service, or software component.</enum>
-                        <enum value="uri">A Uniform Resource Identifier (URI) is for an interconnection, service, or software component.</enum>
+            &allowed-values-property-name-networked-components;
                   </allowed-values>
                   <allowed-values target="[@type=('service', 'software')]/prop[has-oscal-namespace('http://csrc.nist.gov/ns/oscal')]/@name">
-                        <enum value="ipv4-address">The Internet Protocol Version 4 address is for an interconnection, service, or software component.</enum>
-                        <enum value="ipv6-address">The Internet Protocol Version 6 address is for an interconnection, service, or software component.</enum>
-                        <enum value="direction">The direction categorizes the network connectivity of an interconnection, service, or software component.</enum>
-                        <enum value="uri">A Uniform Resource Identifier (URI) is for an interconnection, service, or software component.</enum>
+            &allowed-values-property-name-networked-components;                        
                   </allowed-values> 
                   <allowed-values target="prop[has-oscal-namespace('http://csrc.nist.gov/ns/oscal') and @name=('ipv4-address','ipv6-address')]/@class">
                         <enum value="local">The identified IP address is for this system.</enum>

src/metaschema/shared-constraints/allowed-values-property-name-networked-components.ent

@@ -0,0 +1,4 @@
+<enum value="ipv4-address">The Internet Protocol Version 4 address is for an interconnection, service, or software component.</enum>
+<enum value="ipv6-address">The Internet Protocol Version 6 address is for an interconnection, service, or software component.</enum>
+<enum value="direction">The direction categorizes the network connectivity of an interconnection, service, or software component.</enum>
+<enum value="uri">A Uniform Resource Identifier (URI) is for an interconnection, service, or software component.</enum>