Fix k8s entrypoint management for build container
Summary
Steps to reproduce
This issue is to make sure that the changes made in the MRs below are re introduced in %17.0
- Add custom entrypoint for the build container f... (!4394 - merged) • Baptiste Lalanne • 16.6
- Sanitize image entrypoint to remove empty string (!4452 - merged) • Romuald Atchadé • 16.6
Those MRs changes the behaviour of the executorkubernetes WRT to build
container entrypoint and were thus reverted from the %16.6.
They will be re introduced as breaking change in %17.0
A documentation entry should also be added to warn users in advance.