This commit adds language tags to the following pages, to get
closer to the goal of turning on a fenced code block linting rule
in markdownlint.

The following pages were changed:

       modified:   administration/file_hooks.md
       modified:   administration/pages/source.md
       modified:   administration/raketasks/check.md
       modified:   administration/raketasks/geo.md
       modified:   administration/raketasks/ldap.md
       modified:   administration/raketasks/maintenance.md