docs: standardize env vars to uppercase convention

[MaxBlack-dev]

Description

Standardizes all environment variable references in documentation to use uppercase naming convention (NPM_CONFIG_) instead of lowercase (npm_config_).

Changes

• Changed npm_config_binroot to NPM_CONFIG_BINROOT in scripts.md
• Changed npm_config_prefix to NPM_CONFIG_PREFIX in npm.md (2 instances)
• Changed npm_config_ to NPM_CONFIG_ in npm.md
• Changed npm_config_key to NPM_CONFIG_KEY in npm.md

Fixes

Closes #4891

Rationale

The documentation had inconsistent casing for environment variables - some references used uppercase (NPM_CONFIG_USERCONFIG) while others used lowercase (npm_config_prefix). Following the standard convention, environment variables should always be referenced in uppercase. While npm internally converts both to lowercase, using uppercase in documentation follows the de-facto standard and avoids confusion.

Type of Change

Documentation update

[ryenus]

Wow, finally, thank you @MaxBlack-dev so much for this! 🎉

BTW, I vaguely remember to have seen someone mentioned that when both the lowercase and uppercase environment variables exist, like having both npm_config_userconfig and NPM_CONFIG_USERCONFIG set, then one of the two would take precedence due to the way things have been implemented. I might be wrong though, I wonder if there's any plan to clarify that part as well?