be more precise using common `__prefix_line` expression (set `_daemon` to recognize apache and httpd only)

config/filter.d/apache-common.conf

@@ -22,6 +22,9 @@ apache-prefix-syslog = %(__prefix_line)s
 apache-prefix-logfile = \[\]\s
 apache-prefix-all = (?:%(apache-prefix-logfile)s|%(apache-prefix-syslog)s)?
 
+# Setting for __prefix_line (only `logging=syslog`):
+_daemon = (?:apache\d*|httpd(?:/\w+)?)
+
 apache-prefix = <apache-prefix-<logging>>
 
 _apache_error_client = <apache-prefix>\[(:?error|\S+:\S+)\]( \[pid \d+(:\S+ \d+)?\])? \[client <HOST>(:\d{1,5})?\]