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/developers/plugins/legacy/data-sources.md

@@ -1,7 +1,6 @@
 +++
 title = "Legacy data source plugins"
 keywords = ["grafana", "plugins", "documentation"]
-type = "docs"
 aliases = ["/docs/grafana/latest/plugins/developing/datasources/"]
 +++