Support basic auth in beacon.Client

[kasey]

🐞 Bug Report

Description

beacon.Client hostname handling extracts the hostname and port from the provided hostname argument, but it does not extract the username and password from basicauth, so requests to a beacon node endpoint using basic auth will fail.

Has this worked before in a previous version?

no

🔬 Minimal Reproduction

go run github.com/prysmaticlabs/prysm/cmd/prysmctl checkpoint latest --beacon-node-host='https://$USERNAME:$PASSWORD@eth2-beacon-mainnet.infura.io'

🔥 Error

INFO[0000] requesting http://eth2-beacon-mainnet.infura.io/eth/v1/beacon/weak_subjectivity
INFO[0000] falling back to generic checkpoint derivation, weak_subjectivity API not supported by server
INFO[0000] requesting http://eth2-beacon-mainnet.infura.io/eth/v1/node/version
FATA[0000] unable to proceed with fallback method without confirming node version: error requesting node version: code=401, url=https://eth2-beacon-mainnet.infura.io:443/eth/v1/node/version, body=response body:
project id required

🌍 Your Environment

Operating System:
n/a

What version of Prysm are you running? (Which release)

develop branch