LLM support (2.x)

[ZanSara]

LLM support for v2 implies replicating the functionality of v1's PromptNode.

Ideally we should create several smaller components which can be combined into flexible layouts.

https://www.notion.so/deepsetai/WIP-LLM-Support-in-v2-a19ad6ace3fe436291b9f42e70d32704

Tasks

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1. proposal: LLM support in Haystack 2.0 #5540
   2.x proposal +2
2. PromptBuilder #5622
   2.x +1
   
3. OpenAI LLM Generators for Haystack 2.0 #5623
   2.x +1
   
4. AnswersBuilder #5624
   2.x +1
   
5. Add HuggingFaceTGIGenerator LLM support (2.x) #5625
   2.x +1
   
6. CohereGenerator #5984
   2.x hacktoberfest topic:LLM +3
7. ClaudeGenerator
8. Add SagemakerGenerator haystack-core-integrations#140
   10 of 10
   P1 +1
   
9. DocumentsBuilder #5700
   2.x P2 type:feature +3
   
10. MetadataBuilder #5702
    2.x P3 type:feature +3
    
11. Support function calling in ChatGPTGenerator #5727
    P2 topic:agent +2
12. HuggingFaceLocalGenerator #5953
    2 of 2
    2.x +1
    
13. Add support for Chat LLM models in 2.x #6035
    2.x +1