Use TreeNodeTag for index plan identifier in Spark 3.0

[sezruby]

Feature requested

#178 introduces an identifier for plans which is already modified to apply an index.
The identifier is stored in options of HadoopFsRelation which is ad hoc approach.

Spark 3.0 provides TreeNodeTag feature to keep some values for each plan node.
Therefore, we could utilize the tag for the identifier.

ref) https://github.com/apache/spark/blob/branch-3.0/sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/trees/TreeNode.scala

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