Make Python GraphQL snippets more readable and ensure json is imported

[Dev22603]

Make Python GraphQL snippets more readable and fix json import

This PR solves the #813

This PR updates the python-requests code generator for GraphQL requests to:

• Generate clearer Python snippets where the GraphQL query and variables are separate variables, and
• Always include import json when GraphQL payloads use json.dumps.

Changes

• codegens/python-requests/lib/util/parseBody.js

  • In the graphql branch:

    • Emit a triple-quoted query variable.

    • Convert GraphQL variables to a Python structure (variables) using the existing helper.

    • Build payload as:

      payload = json.dumps({
          "query": query,
          "variables": variables
      })

• codegens/python-requests/lib/python-requests.js

  • Keep the existing logic that imports json for JSON Content-Type.
  • Additionally import json whenever request.body.mode === 'graphql' so GraphQL snippets can always call json.dumps safely.

Rationale

Previously, the GraphQL query and variables effectively ended up inside a single JSON string, which made the generated snippet hard to read and edit.
In some GraphQL cases, json.dumps was used without import json, causing NameError: name 'json' is not defined.
These changes address both readability and that runtime error.

Testing

• npm test python-requests
  • ESLint: no new errors (only existing warnings remain).
  • Newman + Mocha tests for python-requests pass, including the GraphQL case (POST graphql body(json) with raw).
  • Manually verified that the generated GraphQL Python snippet now has query, variables, payload as described above, and includes import json.