Merge module defaults groups docs into one page (#51045)

The information on module defaults groups would be
better alongside the rest of the module defaults docs

Remove the orphaned old doc

docs/docsite/rst/user_guide/module_defaults_config.rst

@@ -1,27 +0,0 @@
-:orphan:
-
-.. _module_defaults_config:
-
-*****************************
-Module Defaults Configuration
-*****************************
-
-Ansible 2.7 adds a preview-status feature to group together modules that share common sets of parameters. This makes
-it easier to author playbooks making heavy use of API-based modules such as cloud modules. By default Ansible ships
-with groups for AWS and GCP modules that share parameters.
-
-In a playbook, you can set module defaults for whole groups of modules, such as setting a common AWS region.
-
-.. code-block:: YAML
-
-    # example_play.yml
-    - hosts: localhost
-      module_defaults:
-        group/aws:
-          region: us-west-2
-      tasks:
-      - aws_s3_bucket_facts:
-      # now the region is shared between both facts modules
-      - ec2_ami_facts:
-          filters:
-            name: 'RHEL*7.5*'

docs/docsite/rst/user_guide/playbooks_module_defaults.rst

@@ -1,3 +1,5 @@
+.. _module_defaults:
+
 Module defaults
 ===============
 
@@ -72,3 +74,30 @@ Setting a default AWS region for specific EC2-related modules::
           region: '{{ my_region }}'
         ec2_vpc_net_facts:
           region: '{{ my_region }}'
+
+.. _module_defaults_groups:
+
+Module defaults groups
+``````````````````````
+
+.. versionadded:: 2.7
+
+Ansible 2.7 adds a preview-status feature to group together modules that share common sets of parameters. This makes
+it easier to author playbooks making heavy use of API-based modules such as cloud modules. By default Ansible ships
+with groups for AWS and GCP modules that share parameters.
+
+In a playbook, you can set module defaults for whole groups of modules, such as setting a common AWS region.
+
+.. code-block:: YAML
+
+    # example_play.yml
+    - hosts: localhost
+      module_defaults:
+        group/aws:
+          region: us-west-2
+      tasks:
+      - aws_s3_bucket_facts:
+      # now the region is shared between both facts modules
+      - ec2_ami_facts:
+          filters:
+            name: 'RHEL*7.5*'