All of the variables need to be prefixed with REACT_APP_
Mainnet values:
DEFAULT_PROVIDER_URL: https://api.avax.network/ext/bc/C/rpc
DEFAULT_BLOCK_EXPLORER_URL: https://snowtrace.io
DEFAULT_CHAIN_ID: 43114
DEFAULT_CHAIN_NAME: Avalanche Mainnet
SENTRY_DSN: The DSN for sentry
ENVIRONMENT: DEV or PROD
PROOF_KEY: Set this just to a string; change it if you want to invalidate cached proofs (e.g. when a new version of the proof verifier gets deployed)