Replace sys.exit in conda_build.build.bundle_conda

[kenodegard]

Description

Replacing sys.exit call in bundle_conda with the new CondaBuildUserError exception for better downstream error handling. Add missing unit test.

Xref #4209

Checklist - did you ...

• Add a file to the news directory (using the template) for the next release's release notes?
• Add / update necessary tests?
• Add / update outdated documentation?

[codspeed-hq]

CodSpeed Performance Report

Merging #5367 will not alter performance

_{Comparing kenodegard:remove-sys.exit-bundle_conda (d416002) with main (bf79003)}

Summary

✅ 3 untouched benchmarks