Feature Request: Add EnvDefault support in MetaProcess.

[Plutolio777]

Summary

Ergo's environment variable management is exceptionally well-implemented, allowing me to conveniently control environment variables for processes at different levels.

However, during my usage, I noticed that the MetaProcess interface only provides the Env and EnvList methods. I understand that MetaProcess uses the parent process's environment variables and cannot modify them, but if an EnvDefault(name gen.Env, defaultValue any) method could be provided, it would make using environment variables in MetaProcess much more convenient for me.

[halturin]

Thanks for the report. Totally agree, it should have been added to MetaProcess as well. Missed that.

I've just added it to v320 branch