docs: update governance proposal tutorial

[ryanchristo]

Description

Closes: #1748

This pull request updates the existing currency allowlist proposal tutorial to be a message-based governance proposal tutorial with multiple examples of message-based governance proposals including:

• add credit type
• add marketplace denom
• grant authorization

Deploy preview:

• https://deploy-preview-1991--regen-ledger-docs.netlify.app/tutorials/user/message-based-governance-proposals.html

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