Change OAuth settings names and auto configure custom OAuths

i18n/en.i18n.json

packages/rocketchat-custom-oauth/custom_oauth_server.coffee

packages/rocketchat-gitlab/common.coffee

packages/rocketchat-lib/package.js

...ges/rocketchat-lib/settings/server/addOAuthService.coffee

packages/rocketchat-lib/settings/server/startup.coffee

...ages/rocketchat-lib/settings/server/updateServices.coffee

server/startup/migrations/v18.coffee