Automated snippet conversion by scripts

These changes are purely mechanical to differentiate them from manual
fixes/adjustments made in the next commit.
This results in broken code as some snippets contain errors.

Made in four steps:
1. Run ./migrate-snippet.py that converts `.md` files to code files
   and perhaps adds missing lines under `// @hide` comments.
2. Sort Java imports.
3. Remove old `.md` files.
4. Run ./generate.md to produce `*/generated/*.md` files.

qdrant-landing/content/documentation/headless/snippets/collection-aliases/delete/bash.sh

@@ -0,0 +1,11 @@
+curl -X POST http://localhost:6333/collections/aliases \
+  -H 'Content-Type: application/json' \
+  --data-raw '{
+    "actions": [
+        {
+            "delete_alias": {
+                "alias_name": "production_collection"
+            }
+        }
+    ]
+}'