Rename Gogs to Gitea, DRY the controller and improve views

app/assets/images/gogs-logo.svg

app/controllers/application_controller.rb

app/controllers/import/gitea_controller.rb

app/controllers/import/github_controller.rb

app/controllers/import/gogs_controller.rb

app/helpers/import_helper.rb

app/services/projects/import_service.rb

app/views/import/gitea/new.html.haml

app/views/import/gitea/status.html.haml

app/views/import/gogs/new.html.haml

app/views/projects/new.html.haml

app/views/shared/icons/_go_logo.svg.erb

changelogs/unreleased/22348-gitea-importer.yml

config/initializers/1_settings.rb

config/routes/import.rb

lib/gitlab/current_settings.rb

lib/gitlab/gogs_import/importer.rb

lib/gitlab/gogs_import/milestone_formatter.rb

lib/gitlab/import_sources.rb

spec/controllers/import/gitea_controller_spec.rb