[docs] Replace token contract tutorial with NFT contract tutorial

[critesjosh]

The token contract tutorial has grown in complexity and may no longer be a good introductory contract to cover in a tutorial in the docs.

The NFT contract is simpler, contains less information (so easier for readers to follow and understand) and may be more relevant to builders on Aztec (when thinking about identity use cases).

TODO:

• remove the token contract tutorial from the published docs. Consider just adding the draft tag to the frontmatter so we keep the page and the information for now, but it isn't published. This may be helpful for training the cookbook docs chatbot
• write an NFT tutorial to replace the token contract tutorial