books: add Pro Git (ar) (#13176)

* books: add Pro Git (ar)

Add Arabic translation of Pro Git by Scott Chacon and Ben Straub.
Available at: https://git-scm.com/book/ar/v2

* fix: add (HTML) format tag to Pro Git entry

fpb-lint requires format tags for web-hosted books.
Adding (HTML) to the Pro Git Arabic entry.

* fix: remove duplicate content, keep clean single copy + Git section

* fix-duplicates

* Update Pro Git link to GitHub repository