Replace passing `warnings to exit_json with AnsibleModule.warn` for the few modules (#1033) (#1073)

This is a backport of PR #1033 as merged into main (3e32c12).
SUMMARY
Using exit_json or fail_json for warnings is deprecated in ansible-core>=2.19.0 and will be removed in ansible-core>=2.23.0
Tested with ansible-core 2.19.3 as the latest released version at the time of the start of this PR and with 2.16.0 as the lowest version supported by kubernetes.core 6.x
Resolves: #1031
ISSUE TYPE

Bugfix Pull Request

COMPONENT NAME
k8s_drain
k8s_rollback
k8s_scale
ADDITIONAL INFORMATION
The initial version of this PR covers only the module k8s_drain, with the following commits extended to k8s_rollback
k8s_scale

Reviewed-by: Bianca Henderson <beeankha@gmail.com>
Reviewed-by: Mike Graves <mgraves@redhat.com>

tests/integration/targets/k8s_rollback/tasks/main.yml

@@ -402,12 +402,16 @@
         namespace: "{{ namespace }}"
       register: result
 
+    - name: Debug result
+      debug:
+        var: result
+
     - name: Assert warning is returned for no rollout history
       assert:
         that:
           - not result.changed
-          - result.rollback_info[0].warnings is defined
-          - "'No rollout history found' in result.rollback_info[0].warnings[0]"
+          - result.warnings is defined
+          - "'No rollout history found' in result.warnings[0]"
 
     - name: Create a service for unsupported resource test
       k8s: