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/csharp.cs

@@ -0,0 +1,18 @@
+using Qdrant.Client;
+using Qdrant.Client.Grpc;
+using static Qdrant.Client.Grpc.Conditions;
+
+public class Snippet
+{
+	public static async Task Run()
+	{
+		var client = new QdrantClient("localhost", 6334);
+
+		await client.SearchMatrixPairsAsync(
+		    collectionName: "{collection_name}",
+		    filter: MatchKeyword("color", "red"),
+		    sample: 10,
+		    limit: 2
+		);
+	}
+}