RPC pool - update the list of providers

[mixplat]

Just a quick alert that Quicknode will convert free plans into paid trial ones, which may affect availability. I recommend adding or updating with alternative RPC providers like Chainstack (https://chainstack.com), Alchemy (https://alchemy.com), or others that offer always-free plans.

https://github.com/golemfactory/erc20_payment_lib/blob/470d07e79a07e020204afd49d0e88bc22a1867cd/scenarios/rpc_pool_balancer/config-payments-polygon.toml

[[chain.polygon.rpc-endpoints]]
name = "quiknode.pro"
endpoint = "https://rpc-mainnet.matic.quiknode.pro"
priority = 0
max-timeout-ms = 5000
allowed-head-behind-secs = 120