Add "upgrade to paid tier" to errors.yaml

[themetalfleece]

Description

Recently, celo and mantle on public drpc is failing with the message method is not available on freetier, please upgrade to paid tier - this makes nodecore not switch to our other providers.

This PR adds upgrade to paid tier to retryable-errors.

curl -s -X POST -H "Content-Type: application/json" --data '{"jsonrpc":"2.0","method":"eth_getBlockByNumber","params":["finalized",false],"id":1}' https://mantle.drpc.org

{"id":1,"jsonrpc":"2.0","error":{"message":"method is not available on freetier, please upgrade to paid tier","code":35}}

curl -s -X POST -H "Content-Type: application/json" --data '{"jsonrpc":"2.0","method":"eth_getBlockByNumber","params":["finalized",false],"id":1}' https://celo.drpc.org

{"id":1,"jsonrpc":"2.0","error":{"message":"method is not available on freetier, please upgrade to paid tier","code":35}}

[themetalfleece]

We had another provider-specific error which caused trouble - would it make sense to add a flag to mark all unknown errors as retryable, and log that it happened? This would have helped our provider downtime in both cases. Thanks.