[BIP-387] Give Balancer Maxis ability to add 3rd party rewards to mainnet gauges

PR with Payload

https://github.com/BalancerMaxis/multisig-ops/pull/404

Motivation

We already possess this ability for the L2's. The reason we're requesting it for mainnet is so we can add 3rd party rewards in cases where the gauge will not likely be added to the veBAL voting system.

It's preferable to add 3rd party rewards through Aura when the gauge will be or is already in the voting system because it speeds up the process of "ramping up" emissions on the Aura side. Without BAL emissions there's no need to direct users to Aura and involve Aura governance.

Specification

The DAO Multisig eth:0x10A19e7eE7d7F8a52822f6817de8ea18204F2e4f will interact with the Authorizer 0xA331D84eC860Bf466b4CdCcFb4aC09a1B43F3aE6 with the following inputs:

role: 0x3bf29175652a3f0fac5abb715d0b7fe2e7b597e2e2eff555dac6b21a20a7c83e

which corresponds to the role for calling add_reward verifiable here

account: eth:0xc38c5f97B34E175FFd35407fc91a937300E33860

which corresponds to the Balancer Maxi LM Multisig