[ONCHAIN] Add write and read methods for referrals

[ppelicano]

The main goal is to have the referral flow working. For this we will need a smart contract method to write and read referrals

Referral write method

input parameters:

• referrer wallet address: address (sender)
• jobid: string
• referee wallet address: address
• referee email: string

notes: at least one (referee wallet address or email must be sent for the method to process). The idea is to have an onchain data relation between referrers and the referred candidates/referees.

output parameters:

• transaction hash of the sucessful transaction is enough

Referral read method

input parameters:

• referrer wallet address

output parameters:

• a list of emails and wallet addresses and related jobids that this referrer has referred up to present time. Basically what was written in the write method. Note it is imperative that only referrer can see his/her referrals. The emails should be hidden onchain. Either we use encryption or make sure they are not readable by someone else.