Add Sepolia testnet support

[imollov]

Batch NFT Reveal template:

• Hardhat
  • Add network to config
  • Add all new addresses in helper config
• Frontend
  • Add network to useDapp config
  • Add new VRF addresses to config
  • Update error messages for supported networks
  • Manually test if all features work as expected on the new testnet

Vault Harvester template:

• Add network to hardhat config