Add CI action to update allocations for weekly testnet

[conorsch]

As part of the weekly testnet deploy process, we use galileo to read through the recent Discord history and collect disbursements for those requesting funds via the faucet. Rather than asking a human to run these steps interactively, let's automate that step. The process is documented step by step here: https://github.com/penumbra-zone/penumbra/pull/1658/files#diff-83c75d0833c2c520a465acf2286aad6646d817bc143f82edb12d606b57f97c89L41-L52

We should also stop pinning specific tags in Galileo's Cargo.toml: we can just track main, and respond if and when things break. (Changes such as #15 are substantive; much of the recent galileo history in contrast is bumps to the pinned tags.)

See discussion in penumbra-zone/penumbra#1658 for additional context.

[conorsch]

We aren't carrying over historical Discord allocations anymore, because we've stopped resetting the chain on every release, and instead we are preserving testnet chain state via upgrades.