ui: provide Edit Workspace Env option for GOWORK, GOENV

[hyangah]

According to https://pkg.go.dev/cmd/go#hdr-Environment_variables they are "editable" environment variables.

But since the icon+command is used for the functionality to open the file, Edit Workspace Env command is not accessible for them.

Consider presenting both commands (maybe as a dropdown option if two icons are not allowed)