Docs: refine whats_new_in_v1_2 documentation chapter and translate to russian
- en: https://werf.io/documentation/whats_new_in_v1_2/how_to_migrate_from_v1_1_to_v1_2.html
- ru: https://ru.werf.io/documentation/whats_new_in_v1_2/how_to_migrate_from_v1_1_to_v1_2.html
(links will be available very soon)