Add utilities for converting TemplateAttributes and Attributes

This change adds several attribute-related utilities that support
converting TemplateAttribute structures to the new Attributes
structure and back. These utilities will be used in the updated
operation payloads to support seamless KMIP 2.0 encodings without
requiring broad payload internal and external usage changes.

Unit tests have been included to cover the new utility functions.

kmip/core/objects.py

@@ -2974,6 +2974,56 @@ class PublicKeyTemplateAttribute(TemplateAttribute):
             names, attributes, Tags.PUBLIC_KEY_TEMPLATE_ATTRIBUTE)
 
 
+def convert_template_attribute_to_attributes(value):
+    if not isinstance(value, TemplateAttribute):
+        raise TypeError("Input must be a TemplateAttribute structure.")
+
+    tag = enums.Tags.ATTRIBUTES
+    if isinstance(value, CommonTemplateAttribute):
+        tag = enums.Tags.COMMON_ATTRIBUTES
+    elif isinstance(value, PrivateKeyTemplateAttribute):
+        tag = enums.Tags.PRIVATE_KEY_ATTRIBUTES
+    elif isinstance(value, PublicKeyTemplateAttribute):
+        tag = enums.Tags.PUBLIC_KEY_ATTRIBUTES
+
+    attribute_values = []
+    for attribute in value.attributes:
+        attribute_tag = enums.convert_attribute_name_to_tag(
+            attribute.attribute_name.value
+        )
+        attribute_value = attribute.attribute_value
+        attribute_value.tag = attribute_tag
+        attribute_values.append(attribute_value)
+
+    return Attributes(attributes=attribute_values, tag=tag)
+
+
+def convert_attributes_to_template_attribute(value):
+    if not isinstance(value, Attributes):
+        raise TypeError("Input must be an Attributes structure.")
+
+    attribute_structures = []
+    for attribute_value in value.attributes:
+        attribute_name = enums.convert_attribute_tag_to_name(
+            attribute_value.tag
+        )
+        attribute_structures.append(
+            Attribute(
+                attribute_name=Attribute.AttributeName(attribute_name),
+                attribute_value=attribute_value
+            )
+        )
+
+    if value.tag == enums.Tags.COMMON_ATTRIBUTES:
+        return CommonTemplateAttribute(attributes=attribute_structures)
+    elif value.tag == enums.Tags.PRIVATE_KEY_ATTRIBUTES:
+        return PrivateKeyTemplateAttribute(attributes=attribute_structures)
+    elif value.tag == enums.Tags.PUBLIC_KEY_ATTRIBUTES:
+        return PublicKeyTemplateAttribute(attributes=attribute_structures)
+    else:
+        return TemplateAttribute(attributes=attribute_structures)
+
+
 # 2.1.9
 class ExtensionName(TextString):
     """