Adds DEX methods to Auth Package

[bernardo-bastos]

Creates DEX methods on the auth package. Here is a brief description of the most important methods:

• NewDexAppClient: Creates a Dex client with the initial configuration. The values to configure it will be later passed via the Helm chart installation.
• NewDexReverseProxy: Creates a reverse proxy for Dex server to avoid exposing it via a virtual service.
• handleDexLogin: Handles Dex Login.
• handleCallback: Handles Dex callback once after the Log in.