Document product integration for adding SSO

Details:

• Standard Big Bang SSO key/values that must be integrated into package
• If package does not support SSO natively, how to integrate with authservice
• How to deploy Big Bang with Keycloak (reference) and have package use internal Keycloak.
• Validating SSO is working properly

NOTES:

• Use PodInfo as the example app in all instructions. We want someone following the documents from beginning to end able to add podinfo into Big Bang.
• Placeholders for docs will be created in this MR. Format is markdown.
• Any overlapping sections in the original package integration doc should be cleaned up with references to this doc. The original may be renamed to package-integration-supported.md.