Document conditions as a Kubernetes concept

**This is a Feature Request**

**What would you like to be added**
- Add a page, or section of an existing page, about _conditions_ in Kubernetes
- Ideally, also mention _reasons_.
- Add a glossary entry that references that section

Extra credit: revise existing mentions such as https://kubernetes.io/docs/concepts/workloads/pods/pod-lifecycle/#pod-conditions to use a [glossary tooltip](https://kubernetes.io/docs/contribute/style/hugo-shortcodes/) for the new entry.

**Why is this needed**
People might want to know what conditions are.
Docs authors might want to use a glossary tooltip for _condition_ rather than explain each time.

**Comments**
Not sure what conditions are? Please read - but _don't_ plagiarize - https://maelvls.dev/kubernetes-conditions/

/language en
/priority backlog
/lifecycle frozen
/sig architecture