Configure usage-based Stripe product IDs (i.e. prices)

[jankeromnes]

Part of #9036

When creating a Stripe usage-based Subscription, we link a Stripe Customer to a Stripe Product via a "Stripe Price" (technically, a different ID depending on EUR or USD currency)

Currently, we hard-code the Stripe Price IDs in code:

gitpod/components/server/ee/src/user/stripe-service.ts

Lines 119 to 123 in 7bf63df

	// FIXME(janx): Use configmap.
	const prices = {
	EUR: "price_1LAE0AGadRXm50o3xjegX0Kd",
	USD: "price_1LAE0AGadRXm50o3rKoktPiJ",
	};

Instead, we should configure them in a server configmap (for preview envs, staging, and production).