Initialize a Metadata struct with the Token Metadata program id.

metadata_id.rs

#[derive(Clone)]
pub struct Metadata;

impl anchor_lang::Id for Metadata {
    fn id() -> Pubkey {
        Pubkey::from_str("metaqbxxUerdq28cj1RbAWkYQm3ybzjb6a8bt518x1s").unwrap()
    }
}