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/distance-matrix/basic/python.py

@@ -0,0 +1,16 @@
+from qdrant_client import QdrantClient, models
+
+client = QdrantClient(url="http://localhost:6333")
+
+client.search_matrix_pairs(
+    collection_name="{collection_name}",
+    sample=10,
+    limit=2,
+    query_filter=models.Filter(
+        must=[
+            models.FieldCondition(
+                key="color", match=models.MatchValue(value="red")
+            ),
+        ]
+    ),
+)