Use a more generic name as there is soon going to be support for PRIVMSG
(see https://github.com/google/alertmanager-irc-relay/pull/1 for
background).
This introduces a backward-incompatible change in the config file for
these two parameters:
- notice_template -> msg_template
- notice_once_per_alert_group -> msg_once_per_alert_group
I am not introducing the new parameters with a deprecation plan since
both parameters are relatively secondary to the core functioning of the
bot (and this is a free time project after all).
Signed-off-by: Luca Bigliardi <shammash@google.com>
