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

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>
Reviewed-by: Alina Buzachis

plugins/modules/k8s_rollback.py

@@ -168,7 +168,9 @@ def perform_action(svc, resource):
             module.params["kind"],
             resource["metadata"]["name"],
         )
-        result = {"changed": False, "warnings": [warn]}
+        if warn:
+            module.warn(warn)
+        result = {"changed": False}
         return result
 
     if module.params["kind"] == "Deployment":