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/update-collection/with-metadata/go.go

@@ -0,0 +1,27 @@
+package snippet
+
+import (
+	"context"
+
+	"github.com/qdrant/go-client/qdrant"
+)
+
+func Main() {
+	client, err := qdrant.NewClient(&qdrant.Config{
+		Host: "localhost",
+		Port: 6334,
+	})
+
+	client.UpdateCollection(context.Background(), &qdrant.UpdateCollection{
+		CollectionName: "{collection_name}",
+		OptimizersConfig: &qdrant.OptimizersConfigDiff{
+			IndexingThreshold: qdrant.PtrOf(uint64(10000)),
+		},
+		Metadata: qdrant.NewValueMap(map[string]any{
+			"my-metadata-field": map[string]any{
+				"key-a": "value-a",
+				"key-b": 42,
+			},
+		}),
+	})
+}