feat: Add XLS 66 Lending Protocol

[realonbebeto]

Summary

Implements XLS-66 (Lending Protocol)

New transaction types (9)

• LoanBrokerSet: A transaction to create a new LoanBroker object.
• LoanBrokerDelete: A transaction to delete an existing LoanBroker object.
• LoanBrokerCoverDeposit: A transaction to deposit First-Loss Capital.
• LoanBrokerCoverWithdraw: A transaction to withdraw First-Loss Capital.
• LoanBrokerCoverClawback: A transaction to clawback the First-Loss Capital. This transaction can only be submitted by the Issuer of the asset.
• LoanSet: A transaction to create a new Loan object.
• LoanDelete: A transaction to delete an existing Loan object.
• LoanManage: A transaction to manage an existing Loan.
• LoanPay: A transaction to make a Loan payment.

New leger entry type

• Loan - On-chain object that captures various Loan terms. It is an agreement between the Borrower and the loan issuer.
• LoanBroker - On-chain object that captures attributes of the Lending Protocol.

Validation

• All the 9 transactions derive ValidateCurrencies
• Additionaly some trasactions implement custom data validations

Registation

• 9 transaction variants added to the TransactionType enum

• Unit tests implemented

• Pending integration tests due to dependency on XLS-65

• Bug fix (non-breaking change which fixes an issue)

• New feature (non-breaking change which adds functionality)

• Breaking change (fix or feature that would cause existing functionality to not work as expected)

• Refactor (non-breaking change that only restructures code)

• Tests (You added tests for code that already exists, or your new feature included in this PR)

• Documentation Updates

• Release