Make all Perl warnings fatal

There are a lot of Perl scripts in the tree, mostly code generation
and TAP tests.  Occasionally, these scripts produce warnings.  These
are probably always mistakes on the developer side (true positives).
Typical examples are warnings from genbki.pl or related when you make
a mess in the catalog files during development, or warnings from tests
when they massage a config file that looks different on different
hosts, or mistakes during merges (e.g., duplicate subroutine
definitions), or just mistakes that weren't noticed because there is a
lot of output in a verbose build.

This changes all warnings into fatal errors, by replacing

    use warnings;

by

    use warnings FATAL => 'all';

in all Perl files.

Discussion: https://www.postgresql.org/message-id/flat/06f899fd-1826-05ab-42d6-adeb1fd5e200%40eisentraut.org

src/test/ldap/LdapServer.pm

@@ -46,7 +46,7 @@ LdapServer - class for an LDAP server for testing pg_hba.conf authentication
 package LdapServer;
 
 use strict;
-use warnings;
+use warnings FATAL => 'all';
 
 use PostgreSQL::Test::Utils;
 use Test::More;

src/test/ldap/t/001_auth.pl

@@ -2,7 +2,7 @@
 # Copyright (c) 2021-2023, PostgreSQL Global Development Group
 
 use strict;
-use warnings;
+use warnings FATAL => 'all';
 
 use FindBin;
 use lib "$FindBin::RealBin/..";

src/test/ldap/t/002_bindpasswd.pl

@@ -2,7 +2,7 @@
 # Copyright (c) 2023, PostgreSQL Global Development Group
 
 use strict;
-use warnings;
+use warnings FATAL => 'all';
 
 use FindBin;
 use lib "$FindBin::RealBin/..";