[Spark] Update V2 Checkpoint feature name to indicate feature complet…

…eness

Now that all V2 Checkpoints are feature complete as per the Delta spec, this updates the table feature name to indicate that it is ready for use.

Closes #2124

GitOrigin-RevId: 8e45e735ef3e1ce071082e1c0833e9157f1c81b5

spark/src/main/scala/org/apache/spark/sql/delta/DeltaConfig.scala

@@ -637,11 +637,9 @@ trait DeltaConfigsBase extends DeltaLogging {
     "must be Serializable"
   )
 
-  val CHECKPOINT_POLICY_CONFIG_KEY = "checkpointPolicy-dev"
-
   /** Policy to decide what kind of checkpoint to write to a table. */
   val CHECKPOINT_POLICY = buildConfig[CheckpointPolicy.Policy](
-    key = CHECKPOINT_POLICY_CONFIG_KEY,
+    key = "checkpointPolicy",
     defaultValue = CheckpointPolicy.Classic.name,
     fromString = str => CheckpointPolicy.fromName(str),
     validationFunction = (v => CheckpointPolicy.ALL.exists(_.name == v.name)),

spark/src/main/scala/org/apache/spark/sql/delta/TableFeature.scala

@@ -517,12 +517,9 @@ object IcebergCompatV1TableFeature extends WriterFeature(name = "icebergCompatV1
 /**
  * V2 Checkpoint table feature is for checkpoints with sidecars and the new format and
  * file naming scheme.
- * This is still WIP feature.
  */
 object V2CheckpointTableFeature
-  extends ReaderWriterFeature(
-    name = "v2Checkpoint-under-development"
-  )
+  extends ReaderWriterFeature(name = "v2Checkpoint")
   with FeatureAutomaticallyEnabledByMetadata {
 
   override def automaticallyUpdateProtocolOfExistingTables: Boolean = true