[SPARK] Add SQL metrics for ConvertToDelta (delta-io#3841)

#### Which Delta project/connector is this regarding?

- [x] Spark
- [ ] Standalone
- [ ] Flink
- [ ] Kernel
- [ ] Other (fill in here)

## Description

Add the metric "numConvertedFiles" to the ConvertToDelta command node

## How was this patch tested?

Added a new test validating the values

## Does this PR introduce _any_ user-facing changes?

The metric become visible in the plan (i.e. Spark UI)

spark/src/main/scala/org/apache/spark/sql/delta/commands/ConvertToDeltaCommand.scala

@@ -34,13 +34,15 @@ import org.apache.spark.sql.delta.sources.{DeltaSourceUtils, DeltaSQLConf}
 import org.apache.spark.sql.delta.util._
 import org.apache.hadoop.fs.{FileSystem, Path}
 
+import org.apache.spark.SparkContext
 import org.apache.spark.internal.MDC
 import org.apache.spark.sql.{AnalysisException, Row, SparkSession}
 import org.apache.spark.sql.catalyst.TableIdentifier
 import org.apache.spark.sql.catalyst.analysis.{Analyzer, NoSuchTableException}
 import org.apache.spark.sql.catalyst.catalog.{CatalogTable, CatalogTableType, SessionCatalog}
 import org.apache.spark.sql.connector.catalog.{Identifier, TableCatalog, V1Table}
 import org.apache.spark.sql.execution.command.LeafRunnableCommand
+import org.apache.spark.sql.execution.metric.{SQLMetric, SQLMetrics}
 import org.apache.spark.sql.types.StructType
 
 /**
@@ -76,6 +78,11 @@ abstract class ConvertToDeltaCommandBase(
   protected lazy val icebergEnabled: Boolean =
     conf.getConf(DeltaSQLConf.DELTA_CONVERT_ICEBERG_ENABLED)
 
+  override lazy val metrics: Map[String, SQLMetric] = Map (
+    "numConvertedFiles" ->
+      SQLMetrics.createMetric(SparkContext.getOrCreate(), "number of files converted")
+  )
+
   protected def isParquetPathProvider(provider: String): Boolean =
     provider.equalsIgnoreCase("parquet")
 
@@ -380,16 +387,18 @@ abstract class ConvertToDeltaCommandBase(
 
       val numFiles = targetTable.numFiles
       val addFilesIter = createDeltaActions(spark, manifest, partitionFields, txn, fs)
-      val metrics = Map[String, String](
+      val transactionMetrics = Map[String, String](
         "numConvertedFiles" -> numFiles.toString
       )
+      metrics("numConvertedFiles") += numFiles
+      sendDriverMetrics(spark, metrics)
       val (committedVersion, postCommitSnapshot) = txn.commitLarge(
         spark,
         addFilesIter,
         Some(txn.protocol),
         getOperation(numFiles, convertProperties, targetTable.format),
         getContext,
-        metrics)
+        transactionMetrics)
     } finally {
       manifest.close()
     }

spark/src/test/scala/org/apache/spark/sql/delta/ConvertToDeltaSQLSuite.scala

@@ -19,6 +19,7 @@ package org.apache.spark.sql.delta
 import org.apache.spark.sql.delta.sources.DeltaSQLConf
 import org.apache.spark.sql.delta.test.DeltaSQLCommandTest
 
+import org.apache.spark.sql.execution.command.ExecutedCommandExec
 import org.apache.spark.sql.functions.{col, from_json}
 
 trait ConvertToDeltaSQLSuiteBase extends ConvertToDeltaSuiteBaseCommons
@@ -58,6 +59,23 @@ trait ConvertToDeltaSQLSuiteBase extends ConvertToDeltaSuiteBaseCommons
     }
   }
 
+  for (numFiles <- Seq(1, 7)) {
+    test(s"numConvertedFiles metric ($numFiles files)") {
+      val testTableName = "test_table"
+      withTable(testTableName) {
+        spark.range(end = numFiles).toDF("part").withColumn("data", col("part"))
+          .write.partitionBy("part").mode("overwrite").format("parquet").saveAsTable(testTableName)
+
+        val plans = DeltaTestUtils.withPhysicalPlansCaptured(spark) {
+          convertToDelta(testTableName, Some("part long"))
+        }
+
+        // Validate that the command node has the correct metrics.
+        val commandNode = plans.collect { case exe: ExecutedCommandExec => exe.cmd }.head
+        assert(commandNode.metrics("numConvertedFiles").value === numFiles)
+      }
+    }
+  }
 }
 
 class ConvertToDeltaSQLSuite extends ConvertToDeltaSQLSuiteBase