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/inference/openai-upsert/csharp.cs

@@ -0,0 +1,28 @@
+using Qdrant.Client;
+using Qdrant.Client.Grpc;
+
+public class Snippet
+{
+	public static async Task Run()
+	{
+		var client = new QdrantClient(
+		host: "xyz-example.qdrant.io", port: 6334, https: true, apiKey: "<your-api-key>");
+
+		await client.UpsertAsync(
+		    collectionName: "{collection_name}",
+		    points: new List<PointStruct>
+		    {
+		        new()
+		        {
+		            Id = 1,
+		            Vectors = new Document()
+		            {
+		                Model = "openai/text-embedding-3-large",
+		                Text = "Recipe for baking chocolate chip cookies",
+		                Options = { ["openai-api-key"] = "<YOUR_OPENAI_API_KEY>", ["dimensions"] = 512 },
+		            },
+		        },
+		    }
+		);
+	}
+}