astro:env docs should explain which environment variables are captured at build vs runtime

[jyasskin]

📚 Subject area/topic

environment variables

📋 Suggested page

https://5-0-0-beta.docs.astro.build/en/guides/environment-variables/#type-safe-environment-variables

📋 General description or bullet points (if proposing new content)

Some values for context and access result in the environment variable being checked and captured at build time, while other values cause the environment variable to only be read at runtime. The documentation should say which is which.

🖥️ Reproduction of code samples in StackBlitz

No response

[sarah11918]

@florian-lefebvre would you be able to comment on this? Is there an improvement we can make to the docs about this?

[florian-lefebvre]

In my opinion, we already talk about this in this section but maybe we emphasize or clarify it?

[sarah11918]

I think that's fine, it's explained! Thank you Florian!