[Delta] Update Coordinated Commits Usage Logs (delta-io#3774)

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#### Which Delta project/connector is this regarding?
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- [x] Spark
- [ ] Standalone
- [ ] Flink
- [ ] Kernel
- [ ] Other (fill in here)

## Description

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- Describe what this PR changes.
- Describe why we need the change.
 
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1. Renames the full error message with 
- `"exceptionString" -> exceptionString(e)` to record the full error
message;
- `"exceptionClass" -> e.getClass.getName` to retain the error class
information.
2. Adds field `registeredCommitCoordinators`.
3. Removes nested JSONizing. 

## How was this patch tested?

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Existed UTs.

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

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No.

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

@@ -21,7 +21,7 @@ import scala.collection.mutable
 
 import org.apache.spark.sql.delta.actions._
 import org.apache.spark.sql.delta.actions.Action.logSchema
-import org.apache.spark.sql.delta.coordinatedcommits.{CommitCoordinatorClient, CoordinatedCommitsUsageLogs, CoordinatedCommitsUtils, TableCommitCoordinatorClient}
+import org.apache.spark.sql.delta.coordinatedcommits.{CommitCoordinatorClient, CommitCoordinatorProvider, CoordinatedCommitsUsageLogs, CoordinatedCommitsUtils, TableCommitCoordinatorClient}
 import org.apache.spark.sql.delta.logging.DeltaLogKeys
 import org.apache.spark.sql.delta.metering.DeltaLogging
 import org.apache.spark.sql.delta.schema.SchemaUtils
@@ -322,6 +322,8 @@ class Snapshot(
           CoordinatedCommitsUsageLogs.COMMIT_COORDINATOR_MISSING_IMPLEMENTATION_WRITE,
           data = Map(
             "commitCoordinatorName" -> coordinatorName.get,
+            "registeredCommitCoordinators" ->
+              CommitCoordinatorProvider.getRegisteredCoordinatorNames.mkString(", "),
             "readVersion" -> version.toString
           )
         )

spark/src/main/scala/org/apache/spark/sql/delta/coordinatedcommits/CoordinatedCommitsUsageLogs.scala

@@ -44,7 +44,7 @@ object CoordinatedCommitsUsageLogs {
   val FS_COMMIT_COORDINATOR_LISTING_UNEXPECTED_GAPS =
     s"$PREFIX.listDeltaAndCheckpointFiles.unexpectedGapsInResults"
 
-  // Usage log emitted when a requested Commit Coordinator implementation is missing
+  // Usage log emitted when a requested Commit Coordinator implementation is missing.
   val COMMIT_COORDINATOR_MISSING_IMPLEMENTATION =
     s"$PREFIX.commitCoordinator.missingImplementation"
 

spark/src/main/scala/org/apache/spark/sql/delta/coordinatedcommits/CoordinatedCommitsUtils.scala

@@ -79,7 +79,12 @@ object CoordinatedCommitsUtils extends DeltaLogging {
         response
       } catch {
         case NonFatal(e) =>
-          recordEvent(Map("exception" -> Utils.exceptionString(e)))
+          recordEvent(
+            Map(
+              "exceptionClass" -> e.getClass.getName,
+              "exceptionString" -> Utils.exceptionString(e)
+            )
+          )
           throw e
       }
     }
@@ -168,7 +173,7 @@ object CoordinatedCommitsUtils extends DeltaLogging {
             "commitCoordinatorName" -> commitCoordinatorStr,
             "registeredCommitCoordinators" ->
               CommitCoordinatorProvider.getRegisteredCoordinatorNames.mkString(", "),
-            "commitCoordinatorConf" -> JsonUtils.toJson(coordinatorConf),
+            "commitCoordinatorConf" -> coordinatorConf,
             "failIfImplUnavailable" -> failIfImplUnavailable.toString
           )
         )