erp5_credential: Update default from 10yr to infinite

   On the implementation 0 dont set stop date on the Assignment

bt5/erp5_credential/PropertySheetTemplateItem/portal_property_sheets/CredentialPreference/preferred_credential_assignment_duration_property.xml

@@ -33,7 +33,7 @@
         </item>
         <item>
             <key> <string>description</string> </key>
-            <value> <string>Validation duration  for assignments created from a credential (Days)</string> </value>
+            <value> <string>Validity duration for assignments created from a credential request, in number of days. A value of 0 means an infinite duration.</string> </value>
         </item>
         <item>
             <key> <string>id</string> </key>
@@ -53,7 +53,7 @@
         </item>
         <item>
             <key> <string>property_default</string> </key>
-            <value> <string>python: 3650</string> </value>
+            <value> <string>python: 0</string> </value>
         </item>
         <item>
             <key> <string>write_permission</string> </key>