Add timeout to all protocol commands

[connorjclark]

Some commands already do this (see getRequestContent and _evaluateInContext in the driver). We could benefit from implementing a timeout for all commands.

where: sendCommand in lighthouse-core/gather/connections/connection.js

Would prevent issues like #6287

[connorjclark]

for later

// Protocol timeout failures
  PROTOCOL_TIMEOUT: {
    code: 'PROTOCOL_TIMEOUT',
    message: strings.protocolTimeout,
  },
-----
  protocolTimeout: `Waiting for DevTools protocol response has exceeded the allotted time.`,