dnsdist: Add missing QPSAction

dnsdist: Add missing QPSAction

In 1.2.0 we deprecated the `addQPSLimit()` function, suggesting the
use of `QPSAction()` as a replacement, but the Lua binding for
`QPSAction()` was missing. In addition the documenration was referring
to `QPSLimitAction()` instead of `QPSAction()`.

(cherry picked from commit 8499caafb7eeedd63e0e7db6c79dbbcbe1def320)