Add a reason field to every governance vote

[ValarDragon]

Summary

Governance votes should have a "reason" string field, that could then be displayed by explorers or other governance tooling. The reason field length doesn't need to big, it could be parameterized such that its expected to link to an external site. (So perhaps 128 bytes)

The reason field should be required for validator votes. At worst they can spam it and its not that big of a deal.

Problem Definition

We are in a bad social standard, where most validators are voting without providing a reason. I actually had a github issue (or maybe github comment) from cosmos-prelaunch where we wanted to do this. It was closed, because someone predicted that validators would fill it with spam. I still think this should be re-added, and if its filled with spam thats ok. Its auditable that the validator chose to not provide a reason!

Imo this is a significant improvement to expecting more from validators in votes. If its not desired in the cosmos-SDK, will likely go ahead and implement it in Osmosis.

Proposal

Add a reason string field to governance votes. Make it required for validators to include a reason of at least say 10 characters. (But fully optional for non-validators)

cc @sunnya97

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For Admin Use

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[aaronc]

Partially closed by #11308. If you want to make it required for validators, feel free to open a follow-up PR. Requiring validators to specify a reason though should probably be a gov param so chains could disable it

[ValarDragon]

Seems like we need to make a planned structure for the metadata field to use it as a reason, right?

Can't just have many different ad-hoc formats in use, and make explorers deal with them all. Seems like theres really only three use cases here though: "reason as a string", or "reason as a URL pointing to another site", or "reason as a reference pointing to another on-chain data object".

[aaronc]

We are working on that in coordination with a gov frontend. @nooomski @cmwaters any details you can share?

[tac0turtle]

@ValarDragon are you fine with the metadata field here as reasoning. It seems like it's fine since its a string and can be arbitrary like a reason field would be.

Closing this for now, please reopen if something else is needed