[HGP-37] Epoch 4 CEX connectors poll

A quarterly poll that places centralized exchange connectors into Gold, Silver and Bronze tiers, which define the level of maintenance that the Foundation spends on each connector.

The choices for this poll are the current centralized exchanges which have spot or perpetual connectors in the codebase: https://docs.hummingbot.org/exchanges/

After the poll ends, the top choice is the Gold exchange for the following quarterly epoch. The Foundation will be the official maintainer for this exchange's spot and perpetual connectors, and the Foundation's own engineering team will build and maintain these connectors and improve them by keeping up with exchange upgrades and mapping new functionality added via API. These connectors serve as the "gold standard" template for all other connectors of that type.

The #2, #3, and #4 choices are the Silver exchanges. The Foundation will be the official maintainer for this exchange's spot and perpetual connectors as well. However, these exchanges' connectors will be maintained via community developer bounties, tracking improvements made to the Gold exchange connectors.

The Foundation supports Gold and Silver CEXs by running long-term testing bots for their connectors and providing HBOT rewards to users who answer community questions related to them.

Any other exchange that meets the Minimum Voting Power threshold (100K) is a Bronze exchange. The Foundation does not maintain these exchanges' connectors nor will we allocate bounties for them, but they may be maintained by a member of the community. Exchanges that don't meet the Minimum Voting Power threshold will be removed from the codebase.