[Docs RFC] Add a diagram to show how pricing works for different features.

[billy-the-fish]

Add a section and diagram to https://docs.timescale.com/about/latest/pricing-and-account-management/#charging-for-ha-and-read-replicas that shows how features such as Read replication and HA.

Add a line in https://docs.timescale.com/about/latest/pricing-and-account-management/#timescale-cloud-free-trial-for-the-different-tiers to explain how pricing estimates work after the trial period.