Add query/mutation for SanR NFT Subscription

[IvanIvanoff]

Changes

• Support addresses with multiple SanR NFTs
• Add query and mutation related to SanR NFT subscriptions

Add a query that returns boolean whether the user is eligible for obtaining
SanR NFT subscription. Returns true if the user has an address that holds a valid NFT:

{
  checkSanrNftSubscriptionEligibility
}

Add a mutation that will obtain a SanR NFT subscription, if possible.
It performs the check for eligibility and if it passes - creates the subscription.

mutation{
  obtainSanrNftSubscription {
    type
  }
}

Ticket

Checklist:

• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• I have tried to find clearer solution before commenting hard-to-understand parts of code
• I have added tests that prove my fix is effective or that my feature works