AmazonBedrockGenerator is not imported lazily

[anakin87]

It seems related to #92.

To Reproduce
Install haystack-experimental from main
pip install git+https://github.com/deepset-ai/haystack-experimental@main#egg=haystack-experimental

Import a component
from haystack_experimental.components import OpenAIChatGenerator

Error message

NameError                                 Traceback (most recent call last)
[<ipython-input-5-43c8f3e81d24>](https://localhost:8080/#) in <cell line: 1>()
----> 1 from haystack_experimental.components import OpenAIChatGenerator

3 frames
[/usr/local/lib/python3.10/dist-packages/haystack_experimental/components/__init__.py](https://localhost:8080/#) in <module>
      4 
      5 
----> 6 from .extractors import LLMMetadataExtractor
      7 from .generators.chat import OpenAIChatGenerator
      8 from .retrievers.auto_merging_retriever import AutoMergingRetriever

[/usr/local/lib/python3.10/dist-packages/haystack_experimental/components/extractors/__init__.py](https://localhost:8080/#) in <module>
      3 # SPDX-License-Identifier: Apache-2.0
      4 
----> 5 from haystack_experimental.components.extractors.llm_metadata_extractor import LLMMetadataExtractor, LLMProvider
      6 
      7 _all_ = ["LLMMetadataExtractor", "LLMProvider"]

[/usr/local/lib/python3.10/dist-packages/haystack_experimental/components/extractors/llm_metadata_extractor.py](https://localhost:8080/#) in <module>
     50 
     51 @component
---> 52 class LLMMetadataExtractor:
     53     """
     54     Extracts metadata from documents using a Large Language Model (LLM) from OpenAI.

[/usr/local/lib/python3.10/dist-packages/haystack_experimental/components/extractors/llm_metadata_extractor.py](https://localhost:8080/#) in LLMMetadataExtractor()
    152             generator_api: LLMProvider,
    153             generator_api_params: Optional[Dict[str, Any]]
--> 154     ) -> Union[OpenAIGenerator, AzureOpenAIGenerator, AmazonBedrockGenerator, VertexAIGeminiGenerator]:
    155         """
    156         Initialize the chat generator based on the specified API provider and parameters.

NameError: name 'AmazonBedrockGenerator' is not defined