Better surface Stripe sign-up errors in the UI

[jankeromnes]

Bug description

Follow-up to #12343 / #12376

When testing the PR, we noticed two separate UX problems:

1. When you sign up with a given currency, then cancel, then try to sign up with a different currency, Stripe fails with this error:

Error: You cannot combine currencies on a single customer. This customer has had a subscription, coupon, or invoice item with currency eur

It would be cool to handle this problem specifically, e.g. by preventing existing customers from selecting a different currency, and/or by suggesting that they reach out to Gitpod's support (so that we can de-activate the Stripe customer account, allowing the user to create a new one in a different currency).

2. In general, when an error happens on Stripe sign-up, it is not properly shown in the UI, and is currently only visible in the browser console & in the server logs. It would be nice to show visually in the UI that something went wrong and what can be done about it.

Steps to reproduce

1. Sign up a team up to usage-based in one currency
2. Cancel
3. Try to sign up the same team again but in a different currency (it fails, but shows no error in the UI)

Workspace affected

No response

Expected behavior

It should not be possible to try and sign in again with a different currency. Instead, we could prevent the selection of a different currency, and/or suggest that customers reach out to support if they want to switch to a different currency.

Example repository

No response

Anything else?

No response