Set default mempool to CAT

[rootulp]

Context

The v1 mempool is currently the default.

Problem

CometBFT v1 removed the v1 mempool. Binary Builders is helping us upgrade to Cosmos SDK v0.52 and CometBFT v1 which is planned to be included in celestia-app v4. Therefore celestia-app v4 may not have the v1 mempool. We should de-couple the roll-out of CAT mempool from celestia-app v4. Ideally while we're still on celestia-app v3, we make the CAT mempool the default.

Proposal

Before celestia-app v4:

• [Optional] Provide a convenience make command to enable and disable the CAT mempool (similar to bbr-enable / bbr-disable)
• Encourage node operators on Arabica to switch to the CAT mempool
• Let that bake for a week
• Encourage node operators on Mocha to switch to the CAT mempool
• Let that bake for a week
• Encourage node operators on Mainnet to switch to the CAT mempool
• Let that bake for a week
• Modify docs to use CAT mempool instead of prioritized mempool
• Make CAT the default mempool for new operators: chore: update mempool defaults #4284

[rootulp]

Note an alternative option to the one proposed in this issue is to copy the v1 mempool to Comet BFT v1 and then deploy CAT after we release celestia-app v4.