Add new entities to better document the GLQL REST API

What does this MR do and why?

Add new entities to better document the GLQL REST API

• Add new entities for result, data, field, page_info
• Updates the API to use the result entity
• Add specs
• Update OpenApi V2 schema

API Documentation is being done in a separate MR: Add API documentation for the GLQL REST API end... (!215018 - merged)

References

Related to #573055 (closed), and follows up from Create a new GLQL REST API for Duo integration (!209517 - merged).

How to set up and validate locally

1. Call the API with an appropriate GLQL YAML configuration:

   curl -X POST --location "http://gdk.test:8080/api/v4/glql" --http1.1 \
     -H "Host: gdk.test:8080" \
     -H "PRIVATE-TOKEN: {{privateToken}}" \
     -H "Content-Type: application/json" \
     -d '{
       "glql_yaml": "display: table\nfields: title, state, author, created\nsort: created desc\nlimit: 100\nquery: type = Issue and project = \"gitlab-duo/test\""
     }'

2. Verify that it outputs a valid response on success

3. Verify that it outputs a valid error state on failure

MR acceptance checklist

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