Confluence: Create Development and Maintenance Documentation

Because Confluence will be made available to BB users we need to do our due diligence and create a development and maintenance document which describes how to maintain and upgrade Confluence.

Some examples of DEV & MAINT docs below:

• https://repo1.dso.mil/big-bang/product/packages/monitoring/-/blob/main/docs/DEVELOPMENT_MAINTENANCE.md
• https://repo1.dso.mil/big-bang/product/packages/istio-controlplane/-/blob/main/docs/DEVELOPMENT_MAINTENANCE.md

The document should cover specifically:

• How to upgrade Confluence using Kpt.
• How to test Confluence after the upgrade.
• Any additional information which future engineers may find useful to know. (Pitfalls, gotchas, common issues, etc.)