Auto-generate Reward token adds

[Xeonus]

Build out a Github action that takes the following parameters as input and creates a PR with the relevant json / payload to be loaded to the multi-sig:

• gauge address
• reward token address

The technical specifications / guide for this process can be found here: https://github.com/BalancerMaxis/multisig-ops/blob/add_reward_doc/docs/Adding%20Direct%20Incentives%20to%20Gauges/how_to_add_reward.md

[Xeonus]

Add reward payload builder PR: https://github.com/defilytica/balancer-tools-v2/pull/13