Python: add restore method to chat_prompt_template (microsoft#2495)

### Motivation and Context

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In order to add ways to save and restore a running conversation this
adds a restore method and a property to the ChatPromptTemplate class.

### Description

<!-- Describe your changes, the overall approach, the underlying design.
These notes will help understanding how your code works. Thanks! -->
1. Add messages property which provides a view to the role,
message.template tuple
2. Add restore classmethod that takes the same input as a regular init,
but adds a list of tuples, it then loops through that list and adds each
message.

### Contribution Checklist

<!-- Before submitting this PR, please make sure: -->

- [x] The code builds clean without any errors or warnings
- [x] The PR follows the [SK Contribution
Guidelines](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md)
and the [pre-submission formatting
script](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md#development-scripts)
raises no violations
- [x] All unit tests pass, and I have added new tests where possible
- [x] I didn't break anyone 😄

---------

Co-authored-by: Abby Harrison <54643756+awharrison-28@users.noreply.github.com>
Co-authored-by: Devis Lucato <dluc@users.noreply.github.com>

python/semantic_kernel/semantic_functions/chat_prompt_template.py

@@ -1,7 +1,7 @@
 # Copyright (c) Microsoft. All rights reserved.
 
 from logging import Logger
-from typing import TYPE_CHECKING, List, Optional, Tuple
+from typing import TYPE_CHECKING, Dict, List, Optional, Tuple
 
 from semantic_kernel.semantic_functions.prompt_template import PromptTemplate
 from semantic_kernel.semantic_functions.prompt_template_config import (
@@ -61,3 +61,27 @@ async def render_messages_async(
         rendered_messages.append(("user", latest_user_message))
 
         return rendered_messages
+
+    @property
+    def messages(self) -> List[Dict[str, str]]:
+        """Return the messages as a list of tuples of role and message."""
+        return [
+            {"role": role, "message": message._template}
+            for role, message in self._messages
+        ]
+
+    @classmethod
+    def restore(
+        cls,
+        messages: List[Dict[str, str]],
+        template: str,
+        template_engine: PromptTemplatingEngine,
+        prompt_config: PromptTemplateConfig,
+        log: Optional[Logger] = None,
+    ) -> "ChatPromptTemplate":
+        """Restore a ChatPromptTemplate from a list of role and message pairs."""
+        chat_template = cls(template, template_engine, prompt_config, log)
+        for message in messages:
+            chat_template.add_message(message["role"], message["message"])
+
+        return chat_template