feature(apollo-engine-reporting): Add custom http agent support

[eberhara]

This PR fixes #1836.

This PR enables developers to inject the http agent to be used on the network requests to apollo engine endpoint.

TODO:

• Update CHANGELOG.md with your change (include reference to issue & this PR)
• Make sure all of the significant new logic is covered by tests
• Rebase your changes on master so that they can be merged easily
• Make sure all tests and linter rules pass

[eberhara]

@abernix

[eberhara]

engine: {
  apiKey: 'foo',
  requestAgent: proxyUrl ? new HttpsProxyAgent(proxyUrl) : undefined
},

and it works like a charm!

[eberhara]

@abernix updated! forgot that true wasn't a valid option.

[eberhara]

So the codecov check did not pass, however it is complaining about a file that I did not even touch.

[abernix]

This should be published as 2.2.0-alpha.1!

[yongnicholaskim]

@eberhara Where is your example code:

engine: {
  apiKey: 'foo',
  requestAgent: proxyUrl ? new HttpsProxyAgent(proxyUrl) : undefined
},

located? In the apollo.config.js? Or can it go in my server.js? Because I'd like to use process.env.

engine: {
  apiKey: 'foo',
  schemaTag: "dev-test-proxy",
  requestAgent: process.env.proxyUrl ? new HttpsProxyAgent(process.env.proxyUrl) : false
}