docs: add section on configuring different environments for web frameworks

[leoortizz]

Description

Suggestion to mention parameterized configuration docs from Cloud Functions in Web Frameworks, due to many issues raised before with users that did not know how to configure different .env files when deploying to different projects/environments.

For reference, see: #7631, #8543, #8471

Scenarios Tested

Sample Commands

[egilmorez]

Sorry for the delay (pls don't hesitate to ping internally)!

Is there any existing content we could link to? Is this close to the desired guidance: https://firebase.google.com/docs/functions/config-env?gen=1st#deploying_multiple_sets_of_environment_variables_2?

This sentence feels like it needs a little unpacking with an example, but if a link can help, that would work too.

[egilmorez]

(The 2nd gen version to headline would be https://firebase.google.com/docs/functions/config-env?gen=2nd#deploying_multiple_sets_of_environment_variables)

[leoortizz]

Sorry for the delay (pls don't hesitate to ping internally)!

Is there any existing content we could link to? Is this close to the desired guidance: https://firebase.google.com/docs/functions/config-env?gen=1st#deploying_multiple_sets_of_environment_variables_2?

This sentence feels like it needs a little unpacking with an example, but if a link can help, that would work too.

thanks @egilmorez! I made a few changes based on your feedback, let me know what you think!