MDEV-34168: Extend perror utility to print link to KB page

As all MariaDB Server errors now have a dedicated web page, the
perror utility is extended to include a link to the KB page of
the corresponding error code.

All new code of the whole pull request, including one or several
files that are either new files or modified ones, are contributed
under the BSD-new license. I am contributing on behalf of my
employer Amazon Web Services, Inc.

extra/perror.c

@@ -359,7 +359,8 @@ int main(int argc,char *argv[])
       {
         found= 1;
         if (verbose)
-          printf("MariaDB error code %3d (%s): %s\n", code, name, msg);
+          printf("MariaDB error code %3d (%s): %s\n"
+                 "Learn more: https://mariadb.com/kb/en/e%3d/\n", code, name, msg, code);
         else
           puts(msg);
       }

mysql-test/main/perror-win.result

@@ -3,5 +3,6 @@ Win32 error code 150: System trace information was not specified in your CONFIG.
 OS error code  23:  Too many open files in system
 Win32 error code 23: Data error (cyclic redundancy check).
 MariaDB error code 1062 (ER_DUP_ENTRY): Duplicate entry '%-.192T' for key %d
+Learn more: https://mariadb.com/kb/en/e1062/
 Win32 error code 1062: The service has not been started.
 Illegal error code: 30000

mysql-test/main/perror.result

 Illegal error code: 10000
 MariaDB error code 1062 (ER_DUP_ENTRY): Duplicate entry '%-.192T' for key %d
+Learn more: https://mariadb.com/kb/en/e1062/
 MariaDB error code 1408 (ER_STARTUP): %s: ready for connections.
 Version: '%s'  socket: '%s'  port: %d  %s
+Learn more: https://mariadb.com/kb/en/e1408/
 MariaDB error code 1459 (ER_TABLE_NEEDS_UPGRADE): Upgrade required. Please do "REPAIR %s %`s" or dump/reload to fix it!
+Learn more: https://mariadb.com/kb/en/e1459/
 MariaDB error code 1461 (ER_MAX_PREPARED_STMT_COUNT_REACHED): Can't create more than max_prepared_stmt_count statements (current value: %u)
+Learn more: https://mariadb.com/kb/en/e1461/