Draft: Adding ISTIO Envoy Filter for Airflow Webserver Authentication

This MR is adding a ISTIO Envoy filter for airflow Authentication

Changes which are part of this MR

1. Using default authentication in airflow (No auth) to leverage ISTIO

2. Added an Envoy filter targeting only airflow deployment, any request to airflow webserver will be hijacked by the side car proxy and this custom authentication filter will be executed. This filter will be doing the existing Basic Authentication only, we are are mounting Azure Keyvault in the ISTIO side car to fetch the airflow password to validate the one sent in the request headers [These changes have been deployed and tested against an Azure Environment]

3. Added the airflow webserver configurations

Reference Links:

Base64 Decoder method in Lua

String Split in Lua

Related Issue: #175