Unstructured API Host

I'm using the free 14 day trial as well and changing the Unstructured API Host from https://api.unstructured.io to https://api.unstructuredapp.io fixed this for me.

Some validation and extra instructions to help make it easier to get this right. See also 📌 Add a readme Active

I cannot find any mention any more of https://api.unstructured.io, only https://api.unstructuredapp.io, so maybe they deprecated or redirected for example. Updated field descriptions & defaults + added helptext about how to use for the ddev contrib unstructured add-on as well into there. Thanks!