Add autocomplete and expression button for the special instruction Repeat

[Bouh]

Description

Although expressions are permit it's a raw input without indicator and autocomplete.

Solution suggested

Add the autocomplete and an icon for select the expressions.

[4ian]

Note that the button and selector might not be made to work in a small popover, but we could imagine having a button in the popup to open the edition in a separate, "full screen" (or large) dialog where we can have the entire version of the field (with the button and the selector)