Warn when using the deprecated HEADER_ arguments (#20236)

* Make sure the uri module warns about using the deprecated HEADER_ arguments, so that we can actually deprecate in a future version

* Use module.deprecate

* No need to de-dupe ourselves, looks like it is done somewhere I didn't initially see

lib/ansible/modules/network/basics/uri.py

@@ -413,6 +413,9 @@ def main():
     # currently a bit ugly. (e.g. headers='{"Content-Type":"application/json"}')
     for key, value in six.iteritems(module.params):
         if key.startswith("HEADER_"):
+            module.deprecate('Supplying headers via HEADER_* is deprecated and '
+                             'will be removed in a future version. Please use '
+                             '`headers` to supply headers for the request')
             skey = key.replace("HEADER_", "")
             dict_headers[skey] = value
 

test/integration/targets/uri/tasks/main.yml

@@ -180,7 +180,8 @@
     url: 'http://{{ httpbin_host }}/digest-auth/auth/user/passwd'
     user: user
     password: passwd
-    HEADER_Cookie: "fake=fake_value"
+    headers:
+      Cookie: "fake=fake_value"
 
 - name: test PUT
   uri: