Handle file upload Mime content type (including jsonl extension)

[okorepanov]

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Related Open Issues

#521

Description

The problem was initially raised out of jsonl file uploading, which led to error below:

# OpenAI HTTP Error (spotted in ruby-openai 7.1.0): {"error"=>{"code"=>"invalidPayload", "message"=>"The file has no or an empty content type specified."}}
# Faraday::BadRequestError: the server responded with status 400

Previously there was empty content-type hardcoded value while sending http parameters - https://github.com/alexrudall/ruby-openai/blob/main/lib/openai/http.rb#L91-L94

In order to fix an issue with jsonl file, we were patching the gem in our project, writing something like that:

def multipart_parameters(parameters)
  parameters&.transform_values do |value|
    next value unless value.respond_to?(:close) # File or IO object.

    # Faraday::UploadIO does not require a path, so we will pass it
    # only if it is available. This allows StringIO objects to be
    # passed in as well.
    path = value.respond_to?(:path) ? value.path : nil

    mime_type = path&.end_with?('.jsonl') ? Mime[:json].to_s : ''
    Faraday::UploadIO.new(value, mime_type, path)
  end
end

In scope of this PR I'm trying to handle this logic via usage of MIME::Types (mime-types gem).
In order to jsonl file to be recognised as application/json content type we had to manually register it upon project building, that's why I've created OpenAI::MimeTypes module, where we also call .register to register some custom types (might be extended in future).

I've tested it locally, sending jsonl file for batch purposes - it've worked as expected.