Add header to the Current organization setting in middleware

What does this MR do and why?

next iteration in defining the Current.organization middleware logic

# Logic of setting the Current.organization:
      #   - Request header value from injection on frontend
      #   - TODO: Request header from injection from routing layer
      #     see ideas in https://gitlab.com/gitlab-org/gitlab/-/merge_requests/144811#note_1784126192

• add to gon for frontend use described in #432182 (comment 1765139828)

this means we will be removing the default organization setting logic we introduced for initial iteration.

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Related to #437541 (closed)