add(consensus/network): Add an empty `Parameters` struct in `Network::Testnet` #587

Job	Run time
Check Cargo.lock is up to date	1s
Install zebrad from lockfile without cache on ubuntu-latest	1s
Test stable on ubuntu-latest	1s
Test beta on ubuntu-latest	3s
Check deny.toml bans	1s
Test stable on macos-latest	1s
Check deny.toml bans --features default-release-binaries	6s
Check deny.toml bans --all-features	1s
Check for unused dependencies	3s
Check deny.toml sources	1s
Check deny.toml sources --features default-release-binaries	2s
Check deny.toml sources --all-features	1s
	22s

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