logstash: rename syslog facility to facility_name when it's a string

Such facility ids are generated by NetworkManager but the journalbeat
index mapping is expecting a long (7.15.2)

Related to T3705

site-modules/profile/templates/logstash/filter.conf.erb

@@ -30,6 +30,11 @@ filter {
       }
     }
   } else {
+    if [syslog][facility] !~ /^\d+$/ {
+      mutate {
+        rename => { "[syslog][facility]" => "[syslog][facility_name]" }
+      }
+    }
     if [@metadata][version] {
       mutate {
         add_field => {

[Phabricator Migration user]

Some references in the commit message have been migrated:

• T3705 is now swh/meta#3705 (closed)