Add post-query hydration process for empty nodes

[shuchenliu]

Solving #143 by adding standalone node index for ubergraph dataset to Elasticsearch.

Incidentally, the original trapi query provided in the issue will not return any result based on the most recent ubergraph. A slightly modified query can be used instead to see the hydrated query result:

{
  "message": {
    "query_graph": {
      "edges": {
        "e00": {
          "object": "on",
          "predicates": [
            "biolink:affects"
          ],
          "subject": "sn"
        }
      },
      "nodes": {
        "on": {
          "categories": [
            "biolink:Gene",
            "biolink:Protein"
          ],
          "ids": [
            "NCBIGene:4314"
          ],
          "is_set": false
        },
        "sn": {
          "categories": [
            "biolink:ChemicalEntity"
          ],
          "ids": [
            "CHEBI:48927"
          ],
          "is_set": false
        }
      }
    }
  },
  "parameters": {
    "tiers": [
      1
    ]
  },
  "submitter": "infores:arax"
}

[sentry]

Codecov Report

❌ Patch coverage is 13.63636% with 38 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/retriever/lookup/qgx.py	0.00%	24 Missing ⚠️
...etriever/data_tiers/tier_1/elasticsearch/driver.py	8.33%	11 Missing ⚠️
...ever/data_tiers/tier_1/elasticsearch/transpiler.py	62.50%	2 Missing and 1 partial ⚠️

Files with missing lines	Coverage Δ
...ever/data_tiers/tier_1/elasticsearch/transpiler.py	75.00% <62.50%> (-0.95%)	⬇️
...etriever/data_tiers/tier_1/elasticsearch/driver.py	47.05% <8.33%> (-2.95%)	⬇️
src/retriever/lookup/qgx.py	0.00% <0.00%> (ø)

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