[docs] Snippet graveyard to hold references to old snippets (#27567)

## Summary & Motivation

Add a "snippet graveyard" unlisted docs file to hold references to
snippets that are no longer referenced in the docs. This is to avoid a
problem when building versioned docs wherein:

* master and versioned docs need to build
* when building, they reference an index from snippet names to functions
* the set of keys in that index is built by scanning master
* therefore if all references to an older snippet is removed in master,
it will disappear from the index
* causing the versioned doc build to fail because it can’t find the
snippet it still references in the index

This snippet graveyard file (and perhaps the old snippet files too)
should be removed immediately once a solution is found to the above
problem.

## How I Tested These Changes

Built docs

---------

Co-authored-by: Colton Padden <colton@dagsterlabs.com>

Author: smackesey

docs/content/api/modules.json.gz

@@ -0,0 +1,10 @@
+---
+title: "Snippet graveyard"
+sidebar_position: 200
+unlisted: true
+---
+
+This exists purely to retain snippet references to no longer used snippets,
+which is necessary to allow versioned docs to build. It is a temporary measure.
+
+<CodeExample path="docs_beta_snippets/docs_beta_snippets/guides/components/deployments/12-workspace.yaml" language="YAML" title="my-deployment/workspace.yaml" />

docs/content/api/searchindex.json.gz

@@ -0,0 +1,9 @@
+load_from:
+  - python_file:	
+      relative_path: code_locations/code-location-1/code_location_1/definitions.py	
+      location_name: code_location_1	
+      executable_path: code_locations/code-location-1/.venv/bin/python	
+  - python_file:	
+      relative_path: code_locations/code-location-2/code_location_2/definitions.py	
+      location_name: code_location_2	
+      executable_path: code_locations/code-location-2/.venv/bin/python