Move integrations to the backend

[FelixMalfait]

We should create a custom resolver / graphql query apps to hold the content of the integration page.

You will need to adapt the JSON structure. From/To is too focused on a niche use-case (Zapier), we should optimise the structure for that.

Long-term this will probably evolve and be merged with the OAuth app json and the internal Apps/modules. Let's start with something simple.