Fix getSnapshotIndexMetaData Exception Behavior (#47488)

If we fail to read the global metadata in a snapshot
we would throw `SnapshotMissingException` but wouldn't
do so for the index metadata.
This is breaking SLM tests at a low rate because they
use `SnapshotMissingException` thrown from snapshot status APIs
to wait for a snapshot being gone.
Also, we should be consistent here in general and not leak the
`NoSuchFileException` to the transport layer for index meta.

Closes #46508

Author: original-brownbear

server/src/main/java/org/elasticsearch/repositories/blobstore/BlobStoreRepository.java

@@ -744,7 +744,11 @@ public MetaData getSnapshotGlobalMetaData(final SnapshotId snapshotId) {
 
     @Override
     public IndexMetaData getSnapshotIndexMetaData(final SnapshotId snapshotId, final IndexId index) throws IOException {
-        return indexMetaDataFormat.read(indexContainer(index), snapshotId.getUUID());
+        try {
+            return indexMetaDataFormat.read(indexContainer(index), snapshotId.getUUID());
+        } catch (NoSuchFileException e) {
+            throw new SnapshotMissingException(metadata.name(), snapshotId, e);
+        }
     }
 
     private BlobPath indicesPath() {