Add plan signature validation for Hybrid Scan

[sezruby]

Describe the issue

Currently, Hyperspace only supports creating indexes on a logical relation node. In order to support arbitrary logical plans, plan signature comparison is required for getting candidate indexes. This work is done by #76. In case of hybrid scan, we cannot utilize the "index" signature value in IndexLogEntry which is a composite of FileBasedSignature + PlanSignature, because

• Index signature calculation overhead during the query time
• Delete support - need to identify the deleted files and exclude them in the index signature calculation

153 handles this issue by checking the metadata of source files directly without using the index signature.

As a follow-up, we need to add plan signature validation for hybrid scan accordingly. This could be done by following: 1) Store the plan signature of the source plan separately in IndexLogEntry 2) Compare plan signatures in getCandidateIndex

To Reproduce

Expected behavior

Environment

[imback82]

@sezruby Can you check if this issue can be closed?

[sezruby]

Since we only allow 1 relation and the current plan signature of non-hybrid scan is just using "Relation" node, I think we don't need to consider the query plan(Relation) for Hybrid Scan - until we support #95.