Don't calculate auto-sharding for failure store (#128921) (#128968)

Auto-sharding is not yet implemented for the failure store, so we want
to avoid running this computation. The result of the computation is
currently not used anywhere, but it's better to be on the safe side and
avoid the computation altogether.

(cherry picked from commit 140200d)

# Conflicts:
#	server/src/main/java/org/elasticsearch/action/admin/indices/rollover/TransportRolloverAction.java

Author: nielsbauman

server/src/main/java/org/elasticsearch/action/admin/indices/rollover/TransportRolloverAction.java

@@ -269,7 +269,8 @@ protected void masterOperation(
 
                 AutoShardingResult rolloverAutoSharding = null;
                 final IndexAbstraction indexAbstraction = clusterState.metadata().getIndicesLookup().get(resolvedRolloverTarget.resource());
-                if (indexAbstraction.getType().equals(IndexAbstraction.Type.DATA_STREAM)) {
+                // Failure stores currently don't support auto sharding yet.
+                if (indexAbstraction.getType().equals(IndexAbstraction.Type.DATA_STREAM) && targetFailureStore == false) {
                     DataStream dataStream = (DataStream) indexAbstraction;
                     final Optional<IndexStats> indexStats = Optional.ofNullable(statsResponse)
                         .map(stats -> stats.getIndex(dataStream.getWriteIndex().getName()));