This patch turns the glossary entry for "workloads" into "workload" in
order to be consistent with other terms in the glossary. In addition,
the definition is modified to match what the overlay tip for the
"Workload" tag at the top of the glossary page says, which is
"Applications running on Kubernetes".
A workload is *not* a core object itself. Rather, it is a general
concept. Various other core objects describe different types of
workloads, and the glossary definition is appropriately modified to make
that clear.
Fixes Issue #14107
* Add formal definition of workloads
* Update workload.md
* add light copyedit
More section should not repeat short description. Both are served together on the built page.