[ENH] reference api key from a .env file instead of the source code

[AlabasterAxe]

Description of changes

Previously, the JS example suggested users paste their API key directly into the source code. This PR updates the example to pull it from a .env file and tells the user if one has not been set up.

Another issue was if you attempted to just run the demo, you would get a cryptic auth error from google.

Test plan

How are these changes tested?

• [x] tried without defining a key
• [x] example works after supplying a key

Documentation Changes

Are all docstrings for user-facing APIs updated if required? Do we need to make documentation changes in the docs repository?

[github-actions[bot]]

Reviewer Checklist

Please leverage this checklist to ensure your code review is thorough before approving

Testing, Bugs, Errors, Logs, Documentation

• [ ] Can you think of any use case in which the code does not behave as intended? Have they been tested?
• [ ] Can you think of any inputs or external events that could break the code? Is user input validated and safe? Have they been tested?
• [ ] If appropriate, are there adequate property based tests?
• [ ] If appropriate, are there adequate unit tests?
• [ ] Should any logging, debugging, tracing information be added or removed?
• [ ] Are error messages user-friendly?
• [ ] Have all documentation changes needed been made?
• [ ] Have all non-obvious changes been commented?

System Compatibility

• [ ] Are there any potential impacts on other parts of the system or backward compatibility?
• [ ] Does this change intersect with any items on our roadmap, and if so, is there a plan for fitting them together?

Quality

• [ ] Is this code of a unexpectedly high quality (Readability, Modularity, Intuitiveness)