Fee Tokens Whitelist: Allow modification of multiple denoms in same proposal

[JohnnyWyles]

Background

Transaction fees on Osmosis have been payable in assets other than OSMO since v5. This is managed by the txfee module which specifies a denom to be accepted and an OSMO pool to use as a spot price for the quantity of that denom to accept. Any transaction fees paid in these denoms are collected in the module address and converted into OSMO for distribution to stakers at epoch.

This whitelist was initially set as all OSMO paired tokens with usable liquidity on 1st December 2021. Since this point there have been many new tokens listed on Osmosis that fees could be paid in, enabling new users to fund the transaction fee for their first trade on the chain. This becomes more important with the minimum fee requirement from Proposal 354 being implemented in v15 and so multiple fee tokens should be added to ease the onboarding process for new users.

Initially implemented in #394 currently each denom/pool pairing requires a separate proposal to add which leads to governance spam or the requirement to do this maintenance through software upgrades, neither of which is good practice.

Suggested Design

This message should be expanded to allow multiple records to be added in a single proposal, allowing one proposal to add many new denoms.
Ideally this should also allow removal of records in the same proposal.
Would be useful to add this to the CLI tx gov category rather than accessed solely through the txfees module also.