Spike: Debug custom SSL Certificate issues

Summary

The extension has issues connecting to instances that use a self-signed SSL certificate (not signed by a root authority included in node) (Epic: &6244). The goal of this spike is to create a local environment where the server uses self-signed certificate. In this environment, we are going to test setting up the gitlab.ca, gitlab.cert, gitlab.certKey, and gitlab.ingnoreCertificateErrors.

Output of this spike:

1. Documentation about the current support of self-signed certificates in the README - this will help users to set up their extension. If the extension doesn't support self-signed certificates, we'll document that.
2. Triage of existing issues in &6244
3. If cross-fetch (our library for making HTTPS requests) doesn't support self-signed SSL, this spike will document possible alternatives