PSA(SNS-CLI): Distribution.InitialBalances.(governance → treasury)

This is a quick public service announcement for those preparing an SNS launch or building on top of the sns-cli tool (which is distributed via dfx sns).

For consistency reasons, this PR renames Distribution.InitialBalances.governance as Distribution.InitialBalances.treasury in the sns_init.yaml file structure.

Please be ready to adjust your affected projects soon after this PR is merged.