feat: accept form submissions from the websites over an API endpoint

.env.test

@@ -6,3 +6,7 @@ PANTHER_APP_ENV=panther
 PANTHER_ERROR_SCREENSHOT_DIR=./var/error-screenshots
 # the test client requests http://localhost/
 APP_TRUSTED_HOSTS='^localhost$'
+# The api firewall rejects every request while no key is configured, and .env.local is not
+# loaded in the test environment - so the throwaway key the tests send belongs here.
+# Keep it in sync with ApplicationFormControllerTest::KEY.
+APPLICATION_FORM_API_KEY=test-application-form-api-key