separating #13 into different PRs/commits
fixing the time-deltas to be the updated (shorter) ones: 3, 6, 9, 12
months

Fixes HAL-003

> ## Description
> In order to participate in a token locking process, a user needs to
first invoke the process_init entry point.
> 
> This entry point will create an account with the necessary size to
store the information provided in the next step of the process,
process_create .
> 
> The current version of this program is not checking that the provided
System Program and Rent Sysvar accounts corresponds to the correct
accounts, provided by the Solana Rust SDK.
> 
> Although there was not risk identified due to this lack of
restrictions, it is a good practice to implement this validations to
prevent any unexpected attack vector that might appear later.

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.