feat: Example using psp22 contract - Dao Contract using Psp22

[ndkazu]

Description

Issue #337
This contract implements a Decentralized Autonomous Organization using Psp22.
The key functionalities include:

• Membership Management: It maintains a registry of DAO members.
• Proposal Lifecycle: The contract manages the creation, voting, and execution of proposals. Each proposal includes details like description, voting period, vote tallies, execution status, beneficiary, and amount to be awarded.
• Voting Mechanism: It implements a voting system where members can cast votes with their balance on proposals. The contract tracks voting periods and maintains vote counts for each proposal.
• Token Integration: The DAO is associated with a specific Psp22 token_id.
• Governance Parameters: governance parameters such as voting periods are customizable.
• Vote Tracking: The contract keeps track of when members last voted.
• Proposal Execution: Once a proposal's voting period ends and it passes, the contract handles the execution of the proposal: Transfer funds to the chosen beneficiary.]

ToDo

• Tests
• Events
• in-code documentation

Remark

Considering the fact that another issue is asking for psp22 examples using cross contract call, I decided to use api::... instead of the macro contract_ref!.