[Small Bug] Inconsistent Interface with the NFT Example

[gagdiez]

The current implementation of nft_mint is:

    pub fn nft_mint(
        &mut self,
        token_id: TokenId,
        metadata: TokenMetadata,
        receiver_id: AccountId,
    )

While the one at the NFT example is:

pub fn nft_mint(
        &mut self,
        token_id: TokenId,
        token_owner_id: AccountId,
        token_metadata: TokenMetadata,
    )

This difference in interfaces comes from the fact that nft_mint is not an standardized function in the NFT specs

We need to homogenize the input parameter across both examples, as well as check for other methods to see if there are any further inconsistencies

What needs to be done

• Change the metadata to token_metadata
• Change the receiver_id to token_owner_id
• Check for other inconsistencies on the code and fix them
• Check workflow tests