Add libc6 to Dockerfile in run stage

[AliKarami]

we found that in v5.21.0 there is missing GLIBC_2.28 requirement and pod crashes. so we add libc6 package which solves the issue.

Issue

fix crashes caused by missing GLIBC_2.28 requirement.

Tasklist

• CHANGELOG.md entry (How to write a changelog entry)
• update relevant Wiki pages
• add tests (see testing documentation
• review
• adjust for comments
• cherry pick to release branch

Requirements / Relations

[amirmasud]

The problem seems to be caused by gcc package dependencies where it uses libc6-dev as mentioned here and on run-stage the previous Dockerfile didn't add libc6 and the libc6 version wasn't the same. so by adding the package as @AliKarami did, the problem should be solved.

[danpat]

Ugh. I missed that the Dockerfile depends on buster, which is still testing - dependencies may still change over time. It might be preferable to switch to stretch which is considered stable.

We should also add some tests for this dockerfile to catch this stuff....I'll look into that.

[amirmasud]

Since the libc6 is a dependency of libc6-dev which also is a dependency of gcc we can be sure that it won't cause any further issues in the future :)

[danpat]

I decided to avoid the currently unstable state of buster and go with the downgrade to stretch-slim over in #5338