Add Arabic welcome templates to welcome.py
Add Arabic welcome templates to welcome.py

- Egyptian Arabic Wikipedia (arzwiki)
- Arabic Wikibooks (arwikibooks)
- Arabic Wikisource (arwikisource)

Bug: T210480
Change-Id: Ie4be00dbd3fa90bc27283c60ca7aedca2e969a5a

wikimedia/pywikibot-core,wikimedia/pywikibot-core,PersianWikipedia/pywikibot-core