Potential endpoint for RPC calls

[jurevans]

It would be nice if the indexer API could support relaying RPC calls to a node. Two specific cases would be:

• During Tx building functions, any validation uses the RPC endpoint that was provided when initializing the SDK
• During process_tx / broadcastTx

Would it be possible to have something like a /rpc that proxies RPC calls to a node in the network? Or perhaps we can somehow handle these calls with the indexer to avoid having to provide a separate RPC URL. If we can make this endpoint, we could pass this when initializing the SDK, then remove the need to track the RPC URL.

UPDATE This may not be needed at all, as we can think of multiple ways of improving the experience without setting up a new endpoint