build: Add elasticsearch7 and elasticsearch8 extra

[bogdankostic]

Related Issues

• related to Make ElasticsearchDocumentStore compatible with ES8 #5027

Proposed Changes:

This PR adds the installation extras elasticsearch7 and elasticsearch8 and points the installation extra elasticsearch to elasticsearch7.

How did you test it?

I manually executed pip install .[elasticsearch], pip install .[elasticsearch7], and pip install .[elasticsearch8].

Notes for the reviewer

We decided that with Haystack 1.21, Elasticsearch 8 will become the default one and we will remove the extra elasticsearch8. Instead, the extra elasticsearch will install version 8 of the Elasticsearch client.

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 unit tests and updated the docstrings
• 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

[coveralls]

Pull Request Test Coverage Report for Build 5488535228

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.005%) to 44.794%

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Totals
Change from base Build 5487781909:	0.005%
Covered Lines:	10329
Relevant Lines:	23059

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💛 - Coveralls