[8.13] Adds section about the different options to use NLP in the stack (backport #2679)

[mergify]

Overview

Related issue: https://github.com/elastic/search-docs-team/issues/83
This PR expands the NLP overview section with the NLP in the Elastic stack subsection. This text explains the different options the users have for using NLP:

• NLP models as a service through the Inference API,
• NLP models uploaded and deployed in the cluster,
• store embeddings in an ES vector database.

Preview

NLP in the Elastic stack

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This is an automatic backport of pull request #2679 done by Mergify.

[github-actions]

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