Rename concept section

The term “resource“ is much used and often misleads readers; change it
for something else. This section is really about the concepts in
Kubernetes that let you manage your applications / workloads.

Author: Tim Bannister

content/en/docs/concepts/workloads/controllers/_index.md

@@ -1,5 +1,5 @@
 ---
-title: "Workload Resources"
+title: "Workload Management"
 weight: 20
 simple_list: true
 ---