Set a usage cap on cloud

[timgl]

Some users might want to avoid unpleasant surprises with high bills. It'd be nice to have a way to add a usage cap after which we either lock the interface or stop ingestion (former probably better).

[paolodamico]

Very related to #3127

[samwinslow]

I'd also like to mention that, if we build this, the UI of #7511 should be updated to indicate where the current month's usage stands in relation to that cap.

[aantn]

Just to comment from the perspective of a user, I held off on entering my credit card for a very long time because you can't set a cap.

I'm more than happy to pay for Posthog, but there is something incredibly scary about entering a credit card and not knowing the maximum amount you can be charged.

[mariusa]

Dupes:

https://github.com/PostHog/posthog/issues/3127

https://github.com/PostHog/posthog/issues/9338