Auto-generate markdown command docs (#4451)

* Finish updating

* a couple improvements

* Update renames

* cleanup examples

docs/commands/metadata.md

@@ -0,0 +1,28 @@
+---
+title: metadata
+layout: command
+version: 0.59.0
+---
+
+Get the metadata for items in the stream
+
+## Signature
+
+```> metadata (expression)```
+
+## Parameters
+
+ -  `expression`: the expression you want metadata for
+
+## Examples
+
+Get the metadata of a variable
+```shell
+> metadata $a
+```
+
+Get the metadata of the input
+```shell
+> ls | metadata
+```
+