Update subgraph endpoints

[boyuan-chen]

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Overview

Describe what your Pull Request is about in a few sentences.

Update the subgraph endpoints to Graph Studio.

Graph Studio provides two endpoints. One is for development, which is free. The other requires your own API key. If the API key is not provided in the .env file or environment, we will use the development endpoint.

Changes

Describe your changes and implementation choices. More details make PRs easier to review.

• Update subgraph endpoints
• Clean up the code

Testing

Describe how to test your new feature/bug fix and if possible, a step by step guide on how to demo this.

Updated the unit tests