Mistral Embedders and Generators

[TuanaCelik]

Summary and motivation

Creating this issue for deepset-ai/haystack#6928

Mistral uses the same API as OpenAI and so far we've instructed people to use the OpenAIChatGenerator and OpenAITextEmbedder to make use of the Mistral API directly.

It would be good to have components that wrap these two which makes it nicer to use with Mistral: https://haystack.deepset.ai/integrations/mistral

Detailed design

The components use the OpenAI embedders and generators. Currently mistral uses pretty much the identical API to OpenAI, but we can make changes when and if they move on to something else

Checklist

If the request is accepted, ensure the following checklist is complete before closing this issue.

Tasks

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1. Adding mistral generator and embedders #409
   integration:mistral topic:CI type:documentation +3
   
2. Docs are published at https://docs.haystack.deepset.ai/
3. There is a Github workflow running the tests for the integration nightly and at every PR
4. A label named like integration:<your integration name> has been added to this repo
5. The labeler.yml file has been updated
6. The package has been released on PyPI
7. An integration tile has been added to https://github.com/deepset-ai/haystack-integrations
8. The integration has been listed in the Inventory section of this repo README
9. There is an example available to demonstrate the feature
10. The feature was announced through social media
11. Submit to Mistral Docs

[TuanaCelik]

@dfokina - I've prepared the docs on Notion.
Can I have a review on there please? I'm happy to publish when you see fit 👍