Added custom keys functionality
'docker.env' now accepts GRANDMASTER_PK and SUBNETS_PK. Where SUBNETS_PK can have multiple keys separated by a comma ','. Number of subnet keys must equal NUM_SUBNET. Keys are randomized if not provided.
Added RELAYER_MODE in 'docker.env', CSC deployment will select from 'full' or 'lite' smart contract, default 'full'.
Automate CHECKPOINT_CONTRACT copy-paste step (manual action no longer required).
PARENTCHAIN_WALLET is no longer required in 'docker.env', the address will be derived from PARENTCHAIN_WALLET_PK.
Disabled parentchain observer in docker-compose.yml, unused for now (due to long startup time).