refactor!: extract elasticsearch

[ZanSara]

Related Issues

• fixes Extract elasticsearch #4667
• relative to Extract dependencies from core list #4417

Proposed Changes:

• Extract elasticsearch into an elasticsearch extra and add it to the docstores extra
• Fence off all imports to make them optional

How did you test it?

• CI

Notes for the reviewer

• This is likely to affect many tutorials, examples, snippets, etc etc. Let's try to find everything that is affected by this change.
• Docker images seems to be unaffected ✔️
• TODO update tutorials
• TODO update documentation

Checklist

• I have read the contributors guidelines and the code of conduct
• I have updated the related issue with new insights and changes
• I added tests that demonstrate the correct behavior of the change
• I've used one of the conventional commit types for my PR title: fix:, feat:, build:, chore:, ci:, docs:, style:, refactor:, perf:, test:.
• I documented my code
• I ran pre-commit hooks and fixed any issue

[silvanocerza]

Looks alright to me, I'd wait to merge #4602 before this one though.

Also let's plan all the tutorials and docs edits before merging it maybe.

[ZanSara]

Alright, I'll talk to @TuanaCelik and @bilgeyucel to see how to proceed with the tutorials forst. They have an issue open, but I think we should have a PR ready too. deepset-ai/haystack-tutorials#166

Regarding the docs, I'll check with the docs team and update this thread as well.

[tholor]

Nice, makes sense to carve it out and make MemoryDocumentStore the go-to-doc-store for beginners/tutorials ...!

Quick question: What error message do users see if they try to import ElasticsearchDocumentstore but miss the dependency? Do we give them advise on how to fix it?

[ZanSara]

@tholor they will see the same error they get from all other document stores, so:

Failed to import 'ElasticsearchDocumentStore' which is an optional component in Haystack.
Run 'pip install 'farm-haystack[elasticsearch]'' to install the required dependencies and make this 
component available. (Original error: <the import error>)

See https://github.com/deepset-ai/haystack/blob/main/haystack/utils/import_utils.py#L56-L63 and https://github.com/deepset-ai/haystack/blob/main/haystack/document_stores/elasticsearch.py#L13

[bogdankostic]

I added the elasticsearch extra to this PR of the tutorials repo and made a suggestion on this documentation page, so I think we're good to go.