Bridge: Add support for fallback provider

[njgheorghita]

In the case that the bridge's current provider is unable to respond to requests, the bridge should automagically use a fallback provider. This only applies to pandaops nodes. eg. If the erigon endpoint cannot respond, then the bridge should try the geth endpoint. Optionally, the bridge could have a feature that detects if the optional infura key is available via environment variable, and then use infura as the fallback.