Add estimated infrastructure costs to self host calculator

[corywatilo]

Potential low-hanging fruit to address the issue without changing pricing: add an estimate of infra hosting costs to the self-hosted calculator? This way it should be clear it will cost the same/more to self-host, but also that we're not charging the same for both (which would look bad imo).

This also makes it clear that "managing infrastructure" is something you actively need to think about

Originally posted by @yakkomajuri in https://github.com/PostHog/company-internal/issues/719#issuecomment-1148544217