PKI Certs longtext columns

[satkunas]

Describe the bug
Vanilla MySQL 5.7 complains about the keysize that's generated on 2x longtext columns:

 ERROR 1170 (42000) at line 1479: BLOB/TEXT column 'cn' used in key specification without a key length

ERROR 1170 (42000) at line 1479: BLOB/TEXT column 'serial_number' used in key specification without a key length

To fix this:

 UNIQUE KEY `cn_serial` (`cn`(127),`serial_number`(127)) USING HASH,

We'll need to either use this unique key definition, or reduce the column size for:

CREATE TABLE `pki_certs` (
    `cn` longtext DEFAULT NULL,
    .... 
    `serial_number` longtext DEFAULT NULL,
)....

[satkunas]

Change https://github.com/inverse-inc/packetfence/blob/devel/html/pfappserver/root/src/views/Configuration/pki/certs/schema.js#L29C12-L29C14