Use defer for non-critical scripts

[aduth]

🛠 Summary of changes

Updates non-critical scripts to use defer instead of async.

While both async and defer load scripts without blocking the parser, async will block the parser to execute the script as soon as it's loaded, which may block parsing if it happens before parsing is complete. defer will instead wait for parsing to complete before executing the script, which is acceptable behavior for the scripts affected by the changes in this pull request.

The HTML specification includes helpful diagrams illustrating the difference:

Related resource: https://web.dev/articles/optimizing-content-efficiency-loading-third-party-javascript#async-defer

While this resource includes analytics scripts as an example of async usage, it does so under the premise that these are "important for the script to run earlier in the loading process". It's not clear to me that it's important for these to run early.

📜 Testing Plan

Verify there is no regression in the loading of scripts marked as defer, particularly track-errors.js on http://localhost:3000 should load successfully in default development environments.