Add fallback for Codespace environment variables

[R0Wi]

• Resolves: [Codespaces] Environment variables are not propagated to codespace.config.php anymore #60662

Summary

For some reason when using Github Codepaces, the environment variables are not set and threfore the host overwrite does not work properly.

Resolution notes

• Root cause: getenv() returns false under Apache because Apache is started via sudo service and never inherits the user shell's environment (which is populated by codespaces.sh).
• Fix: When getenv() returns empty (or false), the config now falls back to reading CODESPACE_NAME from environment-variables.json (a file Codespaces always maintains) and defaults GITHUB_CODESPACES_PORT_FORWARDING_DOMAIN to app.github.dev (the fixed GitHub Codespaces domain).

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)
• Labels added where applicable (ex: bug/enhancement, 3. to review, feature component)
• Milestone added for target branch/version (ex: 32.x for stable32)

AI (if applicable)

• The content of this PR was partly or fully generated using AI