Cannot use defer with esbuild (fix: export defer from config)

[ztrange]

Describe the bug
Since esbuild is only able to import stuff from the package's main field, if one tries to use defer in an application and bundle it with esbuild for node, it fails.

Submitting a PR for a failing test for the test suite is ideal.

Expected behavior
Ideally be able to import defer from the main package import, so that bundlers are able to find it.

Please tell us about your environment:

• node-config version: 3.3.9
• node-version: 18

Other information

[markstos]

This was implemented in the branch linked to from #569. That solution included shims so the old paths/names worked.

Someone interested in implementing this could check out that code. The maintainers won't be implementing this though: this PR will need to come from someone who would use the feature.