doc: replay: improve config description

doc: replay: improve config description

First of all, this unordered list for `replay.refAction` introduces
a term with a colon. This is exactly what a description list is,
structurally. Let’s be stylistically consistent and use the desc.
list markup construct. Let’s also drop the harmless but unneeded
indentation.

We can reuse the `::` delimiter since we use an open block.
But for consistency use the typical nested description list
delimiter, namely `;;`.

Second, let’s replace the inline-verbatim `git replay` with a link
to git-replay(1), since we are naming the command. But make that
conditional so that we avoid a self-link inside git-replay(1).[1]

† 1: See e.g. e7b3a768 (doc: git-init: rework config item
     init.templateDir, 2024-03-10) for another example of
     avoiding self-linking

Signed-off-by: Kristoffer Haugsbakk <code@khaugsbakk.name>
Signed-off-by: Junio C Hamano <gitster@pobox.com>