Add a script and a config file to run perlcritic

This is similar to what we do to run perltidy. For now we only run at
severity level 5. Over time we can improve our perl code and reduce the
severity level.

Discussion: https://postgr.es/m/86aa2a3a-0c68-21fb-9560-84ad6914d561@2ndQuadrant.com

src/tools/pgperlcritic/perlcriticrc

+######################################################################
+#
+# src/tools/pgperlcritic/perlcriticrc
+#
+# config  file for perlcritic for Postgres project
+#
+#####################################################################
+
+severity = 5
+
+theme = core
+
+# allow octal constants with leading zeros
+[-ValuesAndExpressions::ProhibitLeadingZeros]

src/tools/pgperlcritic/pgperlcritic

+#!/bin/sh
+
+# src/tools/pgperlcritic/pgperlcritic
+
+test -f src/tools/pgperlcritic/perlcriticrc || {
+	echo could not find src/tools/pgperlcritic/perlcriticrc
+	exit 1
+	}
+
+set -e
+
+# set this to override default perlcritic program:
+PERLCRITIC=${PERLCRITIC:-perlcritic}
+
+# locate all Perl files in the tree
+{
+	# take all .pl and .pm files
+	find . -type f -a \( -name '*.pl' -o -name '*.pm' \) -print
+	# take executable files that file(1) thinks are perl files
+	find . -type f -perm -100 -exec file {} \; -print |
+	egrep -i ':.*perl[0-9]*\>' |
+	cut -d: -f1
+} |
+sort -u |
+xargs $PERLCRITIC \
+	  --quiet \
+	  --program-extensions .pl \
+	  --profile=src/tools/pgperlcritic/perlcriticrc