Give Carreau the ability to mention the backport bot.

Carreau · Carreau · commit a21d19904a9d · 2018-09-21T09:23:40.000+02:00
Mostly because when the backport bot crashes and pull-requests get not
backported he needs to fix the bot and annoy the core dev to re-mention
the bot.

Give Carreau only the ability to mention the bot only for backport (no
other commands). That avoid having him to push a temporary patch on the
bot itself.
diff --git a/.meeseeksdev.yml b/.meeseeksdev.yml
@@ -0,0 +1,4 @@
+users:
+  Carreau:
+    can:
+      - backport

-Original file line number
+Diff line change
@@ @@ -0,0 +1,4 @@ @@
 +users:
 +  Carreau:
 +    can:
 +      - backport