Support for Sns AddGenericNervousSystemFunction for Assets Upgrade

[peterpeterparker]

Either we use similar proposal type as CommitProposedBatchArguments for Juno or we create a custom type.

Links:

• https://internetcomputer.org/docs/current/developer-docs/daos/sns/managing/making-proposals/#addgenericnervoussystemfunction
• https://internetcomputer.org/docs/current/developer-docs/daos/sns/managing/sns-asset-canister/#submitting-an-sns-proposal-and-upgrading-an-asset-canister

[peterpeterparker]

If I ever add those types of proposal, less priority for me given that Juno will differs from those interfaces.