Convert URL paths from /iaf/ to /ff/ to reflect the new name

Currently, the FrankFramework uses `/iaf/` references in the URL paths, pointing to the deprecated name: IAF.
Also the URLs should be updated, to reflect the name changes.

1. This needs to be updated in the documentation as well as in the code.
1. Also it need to be mentioned as breaking change, in the release notes, so end-users are aware of it.
2. The standard deployment URL of de `test` project should be changed from `iaf-test` to `ff-test`.