Add support for X-TOKEN header for gRPC connection

[jhawk28]

Services such as QuickNode support an x-token header for grpc authentication. It would be useful to use a QuickNode specific endpoint for the EVM gateway instead of the public endpoint.

[franklywatson]

Have you tried using the --address-header flag for EVM GW startup? eg:

--address-header=X-TOKEN \

flow-evm-gateway/README.md

Line 200 in 6ccaf58

| `address-header` | `""` | Header for client IP when server is behind a proxy |

[jhawk28]

--address-header is something different. If I were to use grpcurl, it would look like this:

./grpcurl \
  -H "x-token: <token>" \
...

[jhawk28]

something like this needs to be added to

flow-evm-gateway/bootstrap/bootstrap.go

Line 28 in d003e8a

func Start(ctx context.Context, cfg *config.Config) error {

:

	if *token != "" {
		md := metadata.New(map[string]string{"x-token": *token})
		ctx = metadata.NewOutgoingContext(ctx, md)
	}

[m-Peter]

It would be useful to use a QuickNode specific endpoint for the EVM gateway instead of the public endpoint.

Can you elaborate on this? What is the desired outcome/usage of this?

[jhawk28]

We want to be able to set an auth token on our QuickNode endpoint so that we can use a configuration like this:

--access-node-grpc-host=my-quicknode-endpoint.flow-testnet.quiknode.pro:9000
--access-node-grpc-token=2ff605389410fd74640be87d73b4a62782e0eed5