feat: adding mint address validation at create

[wei3erHase]

Fixes HAL-002

Description

After the user invokes the process_init entry point, they need to invoke the process_create entry point to store the necessary information to participate in the token locking process.

A piece of information that the user has to provide is the source token account, where the tokens will be subtracted to participate.

The mentioned token account is not validated to be a token account corresponding to the L3 token, which is expected to be the token used.

As a result, any user can create a vesting_account that does with any token different than L3 token.

The L3 team mentioned that this situation does not represent a risk, since the information on chain will be used on an off-chain process.

However, it is considered a good practice to restrict the functionalities of a program used in production to narrow down the attack surface in order to prevent unexpected behaviors.