Add meta deprecration warning (#910)

* adding deprecation warnings
* fixing imports
* fixing 3.9 linting issues

integrations/amazon_bedrock/src/haystack_integrations/components/generators/amazon_bedrock/chat/chat_generator.py

@@ -1,6 +1,7 @@
 import json
 import logging
 import re
+import warnings
 from typing import Any, Callable, ClassVar, Dict, List, Optional, Type
 
 from botocore.exceptions import ClientError
@@ -135,6 +136,12 @@ def resolve_secret(secret: Optional[Secret]) -> Optional[str]:
         self.stop_words = stop_words or []
         self.streaming_callback = streaming_callback
 
+        warnings.warn(
+            "The `meta` output of the AmazonBedrockChatGenerator will change in the next release to be inline with "
+            "OpenAI `meta`output keys.",
+            stacklevel=2,
+        )
+
     def invoke(self, *args, **kwargs):
         """
         Invokes the Amazon Bedrock LLM with the given parameters. The parameters are passed to the Amazon Bedrock

integrations/anthropic/src/haystack_integrations/components/generators/anthropic/chat/chat_generator.py

@@ -1,5 +1,6 @@
 import dataclasses
 import json
+import warnings
 from typing import Any, Callable, ClassVar, Dict, List, Optional, Union
 
 from haystack import component, default_from_dict, default_to_dict, logging
@@ -114,6 +115,12 @@ def __init__(
         self.client = Anthropic(api_key=self.api_key.resolve_value())
         self.ignore_tools_thinking_messages = ignore_tools_thinking_messages
 
+        warnings.warn(
+            "The `meta` output of the AnthropicChatGenerator will change in the next release to be inline with "
+            "OpenAI `meta`output keys.",
+            stacklevel=2,
+        )
+
     def _get_telemetry_data(self) -> Dict[str, Any]:
         """
         Data that is sent to Posthog for usage analytics.