Auto-generate markdown command docs (#4451)

* Finish updating

* a couple improvements

* Update renames

* cleanup examples

docs/commands/str_upcase.md

@@ -0,0 +1,23 @@
+---
+title: str upcase
+layout: command
+version: 0.59.0
+---
+
+upcases text
+
+## Signature
+
+```> str upcase ...rest```
+
+## Parameters
+
+ -  `...rest`: optionally upcase text by column paths
+
+## Examples
+
+Upcase contents
+```shell
+> 'nu' | str upcase
+```
+