Add signeture of Faraday::Connection#ssl

[rhiroe]

Add Faraday::Connection#ssl signature and Faraday::SSLOptions class.

After merging this Pull Request, the following code passes type checking.

conn = Faraday.new do |builder|
  builder.ssl.client_cert = 'client_cert'
  builder.ssl.client_key = 'client_key'
end

[github-actions]

@rhiroe Thanks for your contribution!

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---

faraday

You changed RBS files for an existing gem.
You need to get approval from the reviewers of this gem.

@yykamei, please review this pull request.
If this change is acceptable, please make a review comment including APPROVE from here.

After that, the PR author or the reviewers can merge this PR.
Just comment /merge to merge this PR.

[yykamei]

Nice!

APPROVE

[yykamei]

/merge