Update HA documentation with reference architecture

The current HA documentation should include a reference architecture that illustrates how geo specific concepts (cursor and tracking databases) interact with HA setups.

• diagram should show primary vs secondary and the different services that run on the secondary
• document the geo specific services and their dependencies (cursor and tracking databases)
• highlight that documentation describes concepts and configuration examples, but as with all HA setups you should use and orchestration tool to achieve your HA objectives