Extend CREATE USER statement to allow HEX strings

When migrating users from mysql to mariadb, the goal was to to migrate them to caching_sha2_password in mariadb with the same hashing so that the password's continue to work.

However we are seeing that there may be hidden characters that may not port hence there is a need to convert them to HEX and create the user on the mariadb side with the HEX value.

Example

mysql> select hex(authentication_string) from mysql.user where user ='user1234';

+----------------------------------------------------------------------------------------------------------------------------------------------+

| hex(authentication_string)                                                                                                                   |

+----------------------------------------------------------------------------------------------------------------------------------------------+

| 244124303035242C7F5F732A1A13472B22173B1E070A167F6E3F793934312F7630482F57434747416F4F6C634B466A2F4151516867522F39626141364D6232686939714C6637 |

+----------------------------------------------------------------------------------------------------------------------------------------------+

1 row in set (0.00 sec)

To use this on the mariadb side, we need to specify that a HEX value is being passed, so a syntax like this needs to be supported.

CREATE USER IF NOT EXISTS 'user1234'@'localhost' IDENTIFIED VIA caching_sha2_password USING x'244124303035242C7F5F732A1A13472B22173B1E070A167F6E3F793934312F7630482F57434747416F4F6C634B466A2F4151516867522F39626141364D6232686939714C6637';

and

CREATE USER IF NOT EXISTS 'user1234'@'localhost' IDENTIFIED VIA caching_sha2_password USING 0x244124303035242C7F5F732A1A13472B22173B1E070A167F6E3F793934312F7630482F57434747416F4F6C634B466A2F4151516867522F39626141364D6232686939714C6637;