contrib/gitdm: add Idan to IBM's group map

According to LinkedIn Idan works at IBM. Please confirm if you want
these contributions counted under IBM or as personal contributions.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Acked-by: Idan Horowitz <idan.horowitz@gmail.com>
Message-Id: <20221219121914.851488-11-alex.bennee@linaro.org>

contrib/gitdm/group-map-ibm

@@ -12,3 +12,4 @@ jcfaracco@gmail.com
 joel@jms.id.au
 sjitindarsingh@gmail.com
 tommusta@gmail.com
+idan.horowitz@gmail.com