Deprecate template parameter for cloudformation (#2048) (#2051)

[PR #2048/5281e89f backport][stable-7] Deprecate template parameter for cloudformation

This is a backport of PR #2048 as merged into main (5281e89).
SUMMARY
The cloudformation module currently directly uses open() to access files passed using the template parameter.  This can be better handled by using template_body and getting folks to use {{ lookup() }}.
The current open based implementation doesn't look in the places that folks might expect to find their files, and doesn't handle templating.  In the event folks aren't delegating everything to localhost, this can also result in files simply not being available.
ISSUE TYPE

Feature Pull Request

COMPONENT NAME
cloudformation
ADDITIONAL INFORMATION

Reviewed-by: Mark Chappell

changelogs/fragments/cloudformation-template.yml

@@ -0,0 +1,2 @@
+deprecated_features:
+  - cloudformation - the ``template`` parameter has been deprecated and will be removed in a release after 2026-05-01.  The ``template_body`` parameter can be used in conjungtion with the lookup plugin (https://github.com/ansible-collections/amazon.aws/pull/2048).

plugins/modules/cloudformation.py

@@ -57,6 +57,8 @@
         must be specified (but only one of them).
       - If I(state=present), the stack does exist, and neither I(template),
         I(template_body) nor I(template_url) are specified, the previous template will be reused.
+      - The I(template) parameter has been deprecated and will be remove in a release after
+        2026-05-01.  It is recommended to use I(template_body) with the lookup plugin.
     type: path
   notification_arns:
     description:
@@ -172,7 +174,9 @@
     state: "present"
     region: "us-east-1"
     disable_rollback: true
-    template: "files/cloudformation-example.json"
+    # The template parameter has been deprecated, use template_body with lookup instead.
+    # template: "files/cloudformation-example.json"
+    template_body: "{{ lookup('file', 'cloudformation-example.json') }}"
     template_parameters:
       KeyName: "jmartin"
       DiskType: "ephemeral"
@@ -188,7 +192,9 @@
     state: "present"
     region: "us-east-1"
     disable_rollback: true
-    template: "roles/cloudformation/files/cloudformation-example.json"
+    # The template parameter has been deprecated, use template_body with lookup instead.
+    # template: "roles/cloudformation/files/cloudformation-example.json"
+    template_body: "{{ lookup('file', 'cloudformation-example.json') }}"
     role_arn: 'arn:aws:iam::123456789012:role/cloudformation-iam-role'
 
 - name: delete a stack
@@ -640,7 +646,13 @@ def main():
         stack_name=dict(required=True),
         template_parameters=dict(required=False, type="dict", default={}),
         state=dict(default="present", choices=["present", "absent"]),
-        template=dict(default=None, required=False, type="path"),
+        template=dict(
+            default=None,
+            required=False,
+            type="path",
+            removed_at_date="2026-05-01",
+            removed_from_collection="amazon.aws",
+        ),
         notification_arns=dict(default=None, required=False),
         stack_policy=dict(default=None, required=False),
         stack_policy_body=dict(default=None, required=False, type="json"),