Ruby/HAML: Extract externalized strings from AST

Currently we extract with by gettext_i18n_rails which is heavily integrated into rails and everything and needs a lot of dependencies in order to fins those strings. An alternative, more slim, approach would be parsing the Ruby and HAML files into an AST and then get the externalized Strings. This is something we do in the Frontend (with gettext-extractor and gettext-extractor-vue)