Docs: updates for file-based menu (#28500)

* initial

* cleanup

* remove bad aliases

* cleanup, fix links

* add docs-file-based-command

* update docs

* update readme

* fix broken links

* fix spelling

Co-authored-by: Diana Payton <52059945+oddlittlebird@users.noreply.github.com>

docs/sources/plugins/_index.md

@@ -1,10 +1,6 @@
 +++
 title = "Plugins"
-type = "docs"
-[menu.docs]
-name = "Plugins"
-identifier = "plugins"
-weight = 1
+weight = 160
 +++
 
 # Plugins

docs/sources/plugins/installation.md

@@ -1,9 +1,6 @@
 +++
 title = "Install plugins"
-type = "docs"
 aliases = ["/docs/plugins/installation/"]
-[menu.docs]
-parent = "plugins"
 weight = 1
 +++