HADOOP-19285. [ABFS] Restore ETAGS_AVAILABLE to abfs path capabilities (#7064)

Caused by HADOOP-19131  

Contributed by: Steve Loughran

Author: steveloughran

hadoop-tools/hadoop-azure/src/main/java/org/apache/hadoop/fs/azurebfs/AzureBlobFileSystem.java

@@ -1686,6 +1686,10 @@ public boolean hasPathCapability(final Path path, final String capability)
     case CommonPathCapabilities.VIRTUAL_BLOCK_LOCATIONS:
       return true;
 
+      // etags are always available on HEAD requests.
+    case CommonPathCapabilities.ETAGS_AVAILABLE:
+      return true;
+     // but etags are only preserved on hns stores.
     case CommonPathCapabilities.ETAGS_PRESERVED_IN_RENAME:
     case CommonPathCapabilities.FS_ACLS:
       return getIsNamespaceEnabled(