Add support for Sierra Leone TIN

[unho]

• It is called Tax Identification Number (TIN) according to https://www.nra.gov.sl/modernisation-programme
  • Also https://oarg.gov.sl/business-register/
  • Also https://mof.gov.sl/wp-content/uploads/2020/02/The-Finance-Act-2020.pdf
• NRA Tax Identification Number (TIN) according to https://www.nra.gov.sl/ (NRA stands for "National Revenue Authority")
• Taxpayer Identification Number according to https://www.nra.gov.sl/taxpayer-identification-number

  The Taxpayer Identification Number, or TIN, is a unique computer-generated number allocated to each taxpayer, whether they are an individual, a commercial business, a Government department, public corporation, or a special body. As its name implies, the TIN identifies taxpayers for the purpose of all their tax and other revenue liabilities, including:

  Goods and Services Tax (GST)
  Income Tax on personal income
  Corporation Tax
  Capital Gains Tax
  Non-tax revenues
  Customs Duties
  Excise Duties
  Property Tax
  The TIN is also required for identification in all other transactions and dealings with the NRA.

• https://org-id.guide/list/SL-NRA

Could not find any example.