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/insert-points/with-custom-shard/rust.rs

@@ -0,0 +1,20 @@
+use qdrant_client::qdrant::{PointStruct, UpsertPointsBuilder};
+use qdrant_client::Payload;
+
+pub async fn main() -> anyhow::Result<()> {
+    client
+        .upsert_points(
+            UpsertPointsBuilder::new(
+                "{collection_name}",
+                vec![PointStruct::new(
+                    111,
+                    vec![0.1, 0.2, 0.3],
+                    Payload::default(),
+                )],
+            )
+            .shard_key_selector("user_1".to_string()),
+        )
+        .await?;
+
+    Ok(())
+}