Group message bootstrapper CLI

[mkysel]

Add group message bootstrapper CLI by logging GM and IU bootstrapper addresses and setting the GM bootstrapper via blockchain.appChainAdmin

• Update CLI in main.go to log both identity update (IU) and group message (GM) bootstrapper addresses in main.getBootstrapperAddress, warn if they differ, and to set both IU and GM bootstrapper addresses in main.setBootstrapperAddress with distinct error handling.
• Extend admin interface and implementation in appchainAdmin.go with blockchain.IAppChainAdmin.GetGroupMessageBootstrapper and blockchain.IAppChainAdmin.SetGroupMessageBootstrapper, persisting to the parameter store and updating the on-chain broadcaster with specific no-op error handling.
• Add parameter key GROUP_MESSAGE_PAYLOAD_BOOTSTRAPPER_KEY in parameterAdmin.go.
• Add tests for GM bootstrapper set/get and edge cases in appchainAdmin_test.go.

📍Where to Start

Start with main.getBootstrapperAddress and main.setBootstrapperAddress in main.go, then review blockchain.appChainAdmin.GetGroupMessageBootstrapper and blockchain.appChainAdmin.SetGroupMessageBootstrapper in appchainAdmin.go.

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Macroscope summarized 873f8e6.

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[mkysel]

Relates to #818. Follow up to #1070