Rename env vars + remove EXPRESS_SESSION_SECRET or document it better?

[maelp]

For now, HyperDX node SDK seems to use EXPRESS_SESSION_SECRET and USAGE_STATS_ENABLED

To avoid collisions with other libs which might use similar generic name, perhaps they should be prefixed with HDX_?

Also it's not clear from the doc what EXPRESS_SESSION_SECRET is about? Does it change only the behavior of the HyperDX UI? Is it something injected in the user Express framework?

And it seems weird that the doc would hardcode such a critical value, and not at least inform users to be careful of changing it when deploying to prod