Add support for Gabon TIN #385

• Seems to be called Numéro d’Identification Fiscale (NIF), also N° du contribuable, and be 6 characters+1 character according to https://www.dgi.ga/object.getObject.do?id=134
• According to the examples in https://www.dgi.ga/fichier-global-des-contribuables the NIF is 4 to 6 digits followed by a letter (clé).
• Seems to be called Numéro d'Identification Fiscal (NIF) according to https://archive.doingbusiness.org/content/dam/doingBusiness/country/g/gabon/GAB.pdf
• Also N° d’identification fiscale

Search online:

• https://www.dgi.ga/fichier-global-des-contribuables
• https://www.dgi.ga/les-assujetis-a-la-tva

Examples:

• Looks like the complete list of taxpayers (or at least 47800 of them): https://www.dgi.ga/fichier-global-des-contribuables
• Plenty of them https://www.dgi.ga/les-assujetis-a-la-tva
• 793 485 N from https://www.cdc-gabon.ga/med/pdf/Manuel_du_Systeme_de_Gestion_Environnementale_et_Sociale_(MSGES)_1627468720362.pdf?_=1627468720
• 790 845 K from https://www.economie.gouv.ga/object.getObject.do?id=2275
• 041165 Z from https://www.economie.gouv.ga/object.getObject.do?id=2021
• 787543 E from https://www.economie.gouv.ga/object.getObject.do?id=2184
• 9941 29 E from http://adag-gouv.ga/uploads/documents/5fec29c1135d4_Avis%20%C3%A0%20manifestation_acquisition%20des%20fournitures_SIG.pdf
• 04682OX from https://ekena.ga/conditions.html
• 780830 E from https://www.moov-africa.ga/Documents/MoovAfrica-GT-Reglement-Startup-Challenge-VF-20210304.pdf