[BUG] Deprecation of OpenSearch DSL format has affected the behavior of the explain API

What is the bug?
Deprecation of OpenSearch DSL format has affected the behavior of the explain API
https://github.com/opensearch-project/sql/issues/3280

Prior to OpenSearch 3.0 we could request DSL syntax using the following query:

POST /_plugins/_sql/_explain?format=json
{"query":"SELECT Shape, _id FROM railroads LIMIT 0,10000"}

result:

{
  "from": 0,
  "size": 10000,
  "_source": {
    "includes": [
      "Shape",
      "_id"
    ],
    "excludes": []
  }
}

With 3.0 we have noticed a couple of issues with our workflow.

1. using format=json returns an error when used with explain API

{
  "error": {
    "reason": "Invalid SQL query",
    "details": "Failed to create executor due to unknown response format: json",
    "type": "IllegalArgumentException"
  },
  "status": 400
}

2. if we dont use format=json then we run into issues with including a geoshape column

POST /_plugins/_sql/_explain
{"query":"SELECT Shape, _id FROM railroads LIMIT 0,10000"}

{
  "error": {
    "reason": "Invalid SQL query",
    "details": "can't resolve Symbol(namespace=FIELD_NAME, name=Shape) in type env",
    "type": "SemanticCheckException"
  },
  "status": 400
}

Start at the SQL explain API endpoint and trace handling for the format=json request and for geoshape field resolution. Compare the documented pre-3.0 behavior with the two OpenSearch 3.0 failures; the work is done when both example explain requests produce valid results without errors.