add(chain): Adds a `network_name` field to `testnet::Parameters` #620

Job	Run time
Build CI Docker / Build images	1s
Check if cached state disks exist for Mainnet / Check if cached state disks exist	1s
Zebra checkpoint update / Run sync-past-checkpoint test	1s
get block template / Run get-block-template test	1s
Generate checkpoints mainnet / Run checkpoints-mainnet test	1s
lightwalletd tip / Run lwd-full-sync test	1s
lightwalletd GRPC tests / Run lwd-grpc-wallet test	1s
Zebra tip JSON-RPC / Run fully-synced-rpc test	1s
lightwalletd tip send / Run lwd-send-transactions test	1s
lightwalletd tip update / Run lwd-update-sync test	1s
submit block / Run submit-block test	1s
Zebra tip update / Run update-to-tip test	1s
	12s

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