Investor onboarding flow: Add explainer in case of whitelisting bug / pending whitelisting transactions

[denniswell]

In case of a failed or pending whitelisting transaction, we currently display all steps as checked but the investor still cannot invest

This screen would only appear in case of a slow transaction or a bug so we should add the following copy:
“Your address is currently being whitelisted. This should only take a couple of minutes. Please contact support@centrifuge.io if you can’t invest after one hour.”

Ideally displayed between the "Subdoc signed" and "ready to invest" step. If not possible or larger effort, fine below "ready to invest"
No fancy UI required, standard grey background box is fine or same design as for other text we display within the steps.