Add script to process Gettext's PO files and generate MO files

REF: https://gitlab.com/gitlab-org/gitlab-ce/issues/28433

Makefile

@@ -21,7 +21,7 @@ all: gitlab-setup gitlab-shell-setup gitlab-workhorse-setup support-setup gitaly
 # Set up the GitLab Rails app
-gitlab-setup: gitlab/.git gitlab-config bundler .gitlab-bundle yarn .gitlab-yarn
+gitlab-setup: gitlab/.git gitlab-config bundler .gitlab-bundle yarn .gitlab-yarn .gettext
 gitlab/.git:
 	git clone ${gitlab_repo} gitlab
@@ -55,6 +55,10 @@ gitlab/public/uploads:
 	cd ${gitlab_development_root}/gitlab && yarn install --pure-lockfile
 	touch $@
+.gettext:
+	cd ${gitlab_development_root}/gitlab && bundle exec rake gettext:pack
+	touch $@
+
 .PHONY:	bundler
 bundler:
 	command -v $@ > /dev/null || gem install $@
@@ -323,3 +327,4 @@ unlock-dependency-installers:
 	.gitlab-bundle \
 	.gitlab-shell-bundle \
 	.gitlab-yarn
+	.gettext