Document how to use custom TLS certificates with management console

Created by: francisschmaltz

3.0 Management console should have to ability to use custom certificates to allow trusted SSL communication to the server. Currently, having the self-signed root cert causes loading issues if HSTS is used on the server normally. This causes the site to fail to load (without ability to proceed) in Chrome and fails to load in Safari.

If the web server uses HSTS for the SSL cert for Sourcegraph (which they should) this causes the issue. If HSTS is disabled in the web server (even though the web server isn't serving the management console) this solves the issues but is NOT a valid workaround (we shouldn't require disabling HSTS to load the management console).

Here is the nginx config line that causes the HSTS error: add_header Strict-Transport-Security. This causes the issue with the management console even if nginx isn't serving the management console.

Allowing a custom cert would solve this issue.