hard fork: update docs to change deploy to Devnet, not Berkeley Testnet

[barriebyron]

update all mentions of Berkeley and zkApp requirements for hard fork Tutorial 3 https://docs.minaprotocol.com/zkapps/tutorials/deploying-to-a-network How to Write a zkApp https://docs.minaprotocol.com/zkapps/how-to-write-a-zkapp zkApps Overview https://docs.minaprotocol.com/zkapps (tuto) Interacting with zkApps server-side https://docs.minaprotocol.com/zkapps/tutorials/interacting-with-zkapps-server-side (and others) including:

Mina zkApps are available only on Berkeley, Mina's public Testnet, now in the final stages of testing before Mainnet. In this tutorial, you deploy a contract to the Berkeley Testnet. Berkeley is feature complete, and only minor changes and bug fixes are expected before Mainnet.

Instead of tutorials using the Berkeley Testnet, switch to Devnet (the Testnet that mimics Mainnet). That way, devs can still get easy access to tMINA through the faucet Block explorer for Devnet https://devnet.minaexplorer.com/

change:

For Berkeley Testnet, the following values:

• Name: berkeley
• URL: https://proxy.berkeley.minaexplorer.com/graphql
• Fee: 0.1

to whatever the values are for Devnet (the ITN)