Add purchasing power parity pricing for Turkey

[tspenov]

Changes

Add purchasing power parity pricing (PPP) API.

    {
      pppSettings {
        isEligibleForPPP
        country
        percentOff
        plans {
          id
          name
          interval
          amount
          product {
            name
          }
        }
      }
    }

Ticket

Checklist:

• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• I have tried to find clearer solution before commenting hard-to-understand parts of code
• I have added tests that prove my fix is effective or that my feature works