The capabilities and documentation for the DFC API are bigger. And since
it's in active development, people want to check the DFC API more
frequently. They needed to find the switch to select the DFC API in the
top right corner but now it's displayed straight away.
Avoids deprecation warnings:
```
DEPRECATION WARNING: swagger_root= is deprecated and will be removed from rswag-api 3.0 (use openapi_root= instead) (called from block in <main> at config/initializers/rswag_api.rb:8)
DEPRECATION WARNING: Rswag::Ui: WARNING: The method will be renamed to "openapi_endpoint" in v3.0 (called from block in <main> at config/initializers/rswag_ui.rb:12)
DEPRECATION WARNING: Rswag::Ui: WARNING: The method will be renamed to "openapi_endpoint" in v3.0 (called from block in <main> at config/initializers/rswag_ui.rb:13)
```
We need to declare in each spec file for which endpoint the spec is
because it was just choosing the first declared one by default. The
first one was v1 and now it's dfc-v1.7.
