Ensure there's no core vs. token bridge ambiguity.
Breaking changes to the CLI:
* "guardiand bridge" CLI is now "guardiand node"
* --solanaBridgeAddress is now --solanaContract
* --bridgeKey is now --guardianKey
The Heartbeat proto message had one of its fields renamed from
BridgeAddress to ContractAddress, but this won't break the wire
format and the only consumer appears to be the CLI.
Change includes a "go mod tidy" - it insisted.
Change-Id: Id8b312827737f07f2d5f3944ebce469d946e7f51
4ac19518bd