Guidance on when to downgrade to a lower site plan to save money

[stevector]

With the updates to pricing and the improved overages policy, I've seen chatter in community channels about when and how to downgrade to a less expensive plan:

• https://community.pantheon.io/forum/t/cost-analysis-for-march-2024-site-plans-and-overage-protection-changes/172
• https://websites.umich.edu/~markmont/public/pantheon-cost-analysis/

I don't want to overload the already in-progress https://github.com/pantheon-systems/documentation/pull/8886 but maybe we should add a page walking through evaluating whether a downgrade makes sense and how to do it.