Prop 682: Set Osmosis-Specific costs to USDC equivalents

This proposal would signal the adjustment of all parameters specifying fees for permissionless but gated tasks specific to Osmosis to be a more stable value.

## Background
Currently, three Osmosis-specific tasks can be performed permissionlessly by paying a fee in OSMO to the Community Pool.

Pool creation, Last modified in Proposal 669 to be 400 OSMO

Creating or adding to a gauge, Implemented in V11 at 50 OSMO and 25 OSMO, respectively.

Both of these costs are designed to be a deterrent to spam whilst also allowing the permissionless use of these features and yielding a small revenue for the community pool.

At the time of setting, these costs were approximately
* Create Pool: 100 USD
* Create Gauge: 50 USD
* Add to Gauge: 25 USD

However, as OSMO price varies over time, these prices at this setting have ranged from:
* Create Pool: 90 USD - 216 USD
* Create Gauge: 11 USD - 82 USD
* Add to Gauge: 6 USD - 41 USD
## Proposal
This proposal signals that costs for Osmosis-specific tasks can be set in an alternative denom decided by governance that is part of the txfee whitelist. This would then be converted to an equivalent OSMO quantity required in order to perform the message on chain.

This proposal signals that this denom should initially be set to USDC via Noble at implementation, and the message costs to be adjusted to:
* Create Pool: 100 USDC
* Create Gauge: 50 USDC
* Add to Gauge: 25 USDC

This maintains a more constant value cost for each message as OSMO price fluctuates.

Non-Osmosis-specific transactions, such as Governance deposits, are not directly covered in this proposal as they are part of the Cosmos SDK, although this proposal signals that this would also be desired.

Accepting non-OSMO assets as payment for these fees is also not directly covered in this proposal but will likely be part of a future proposal.

Forum Thread: https://forum.osmosis.zone/t/set-osmosis-specific-costs-to-usdc-equivalents/622