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/set-payload/by-point-id/rust.rs

@@ -0,0 +1,26 @@
+use qdrant_client::qdrant::{
+    PointsIdsList, SetPayloadPointsBuilder,
+};
+use qdrant_client::Payload,;
+use serde_json::json;
+
+pub async fn main() -> anyhow::Result<()> {
+    client
+        .set_payload(
+            SetPayloadPointsBuilder::new(
+                "{collection_name}",
+                Payload::try_from(json!({
+                    "property1": "string",
+                    "property2": "string",
+                }))
+                .unwrap(),
+            )
+            .points_selector(PointsIdsList {
+                ids: vec![0.into(), 3.into(), 10.into()],
+            })
+            .wait(true),
+        )
+        .await?;
+
+    Ok(())
+}