!feat: allow arbitrary messages in gov proposal

[cmwaters]

THIS IS STILL A WIP :)

Description

Closes: #9438

This is a tracking PR for a set of changes to x/gov:

• Add an array of arbitrary messages to a proposal to be executed if it passes (feat: add array of messages to a proposal #9810)
• Add new proto messages (and module account) for changing params
• Add new proto messages and corresponding methods for the upgrade module
• Update distribution module to handle community spend message
• Add a specific message for TextProposals and remove the existing one
• Remove existing proposal handlers in other modules
• Deprecate Content and remove all usage
• Update simulation / migration

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Outstanding Questions

• For community spends, do we need to introduce a new message or can it be just a MsgTransfer from the community account to the recipients account?
• How can we initialize a chain with certain authorizations i.e gov module is allowed to transfer money from the community pool account?
• In x/params, the parameters are divided into subspaces for each module. Do authorizations have the level of granularity to only allow param changes of a certain subspace?

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Author Checklist

All items are required. Please add a note to the item if the item is not applicable and
please add links to any relevant follow up issues.

I have...

• included the correct type prefix in the PR title
• added ! to the type prefix if API or client breaking change
• targeted the correct branch (see PR Targeting)
• provided a link to the relevant issue or specification
• followed the guidelines for building modules
• included the necessary unit and integration tests
• added a changelog entry to CHANGELOG.md
• included comments for documenting Go code
• updated the relevant documentation or specification
• reviewed "Files changed" and left comments if necessary
• confirmed all CI checks have passed

Reviewers Checklist

All items are required. Please add a note if the item is not applicable and please add
your handle next to the items reviewed if you only reviewed selected items.

I have...

• confirmed the correct type prefix in the PR title
• confirmed ! in the type prefix if API or client breaking change
• confirmed all author checklist items have been addressed
• reviewed state machine logic
• reviewed API design and naming
• reviewed documentation is accurate
• reviewed tests and test coverage
• manually tested (if applicable)

[cmwaters]

Closing this in favour of using ZenHub to track progress of the governance updates