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/java.java

@@ -0,0 +1,25 @@
+package com.example.snippets_amalgamation;
+
+import static io.qdrant.client.ConditionFactory.matchKeyword;
+
+import io.qdrant.client.QdrantClient;
+import io.qdrant.client.QdrantGrpcClient;
+import io.qdrant.client.grpc.Common.Filter;
+import io.qdrant.client.grpc.Points.SearchMatrixPoints;
+
+public class Snippet {
+        public static void run() throws Exception {
+                QdrantClient client =
+                    new QdrantClient(QdrantGrpcClient.newBuilder("localhost", 6334, false).build());
+
+                client
+                    .searchMatrixPairsAsync(
+                        Points.SearchMatrixPoints.newBuilder()
+                            .setCollectionName("{collection_name}")
+                            .setFilter(Filter.newBuilder().addMust(matchKeyword("color", "red")).build())
+                            .setSample(10)
+                            .setLimit(2)
+                            .build())
+                    .get();
+        }
+}