Auto-generate markdown command docs (#4451)

* Finish updating

* a couple improvements

* Update renames

* cleanup examples

docs/commands/str_rpad.md

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+---
+title: str rpad
+layout: command
+version: 0.59.0
+---
+
+pad a string with a character a certain length
+
+## Signature
+
+```> str rpad ...rest --length --character```
+
+## Parameters
+
+ -  `...rest`: optionally check if string contains pattern by column paths
+ -  `--length {int}`: length to pad to
+ -  `--character {string}`: character to pad with
+
+## Examples
+
+Right pad a string with a character a number of places
+```shell
+> 'nushell' | str rpad -l 10 -c '*'
+```
+
+Right pad a string with a character a number of places
+```shell
+> '123' | str rpad -l 10 -c '0'
+```
+
+Use rpad to truncate a string
+```shell
+> '123456789' | str rpad -l 3 -c '0'
+```
+
+Use rpad to pad Unicode
+```shell
+> '▉' | str rpad -l 10 -c '▉'
+```
+