Implement Contract initialization

[miguelnietoa]

Objective

Implement the initialize function in the contract.

Note
This contract should be able to set the DID attributes on initialization. However, the contract will not receive the DID attributes for now. Once the function to set the DID attributes is implemented, the initialize function will need to be updated.

Checklist

• Receive admin and DID method.
• Perform base32 encoding in Rust without relying on external crates.
• Generate a random DID method-specific ID, encode it in base32, and return it within the initialize function.
• Add tests.