Migrate to external Form Service

[sdmcraft]

The Helix Forms Service is deprecated, we should envision a migration away from it in the medium term. For B2B like this site Marketo might be a viable alternative, or a self-hosted forms service.

cc @jalagari

[bosschaert]

As Sunstar is already using Power Automate, PA could also be used to handle the form submissions. It requires a small change to the forms block and the addition of a paUrl to the forms definition xlsx sheet, but the .docx files showing the forms can stay the same.
Example of the changed forms block: https://github.com/bosschaert/sunstar-foundation/blob/form-pa/blocks/form-pa/form-pa.js#L65