Use CentOS base image

What does this MR do?

This change updates the Docker base image to use CentOS 8. The alpine version of the rpm package uses a crypto interface that is not FIPS compliant.

This can be seen using:

モ docker run -it --rm --entrypoint sh registry.gitlab.com/gitlab-org/security-products/analyzers/klar:2 -c 'echo -n FIPS:;cat /proc/sys/crypto/fips_enabled; rpm -q rpm'
Unable to find image 'registry.gitlab.com/gitlab-org/security-products/analyzers/klar:2' locally
2: Pulling from gitlab-org/security-products/analyzers/klar
c9b1b535fdd9: Pull complete
eb567f3f7383: Pull complete
debc2172f28d: Pull complete
4a25ba6b248f: Pull complete
016d9438d1e8: Pull complete
Digest: sha256:3561b09a77f15bcb78479e2b5306725c47633ee4381c2590aedddb48cdb00946
Status: Downloaded newer image for registry.gitlab.com/gitlab-org/security-products/analyzers/klar:2
FIPS:1
error: Failed to initialize NSS library

A detailed rationale for this change can be found here.

The max size of a Docker image is specified as 1.46 GB here:

• https://docs.gitlab.com/ee/development/integrations/secure.html#image-size

What are the relevant issue numbers?

• gitlab-org/gitlab#263482 (closed)

Does this MR meet the acceptance criteria?

• Changelog entry added
• Documentation created/updated for GitLab EE, if necessary
• Documentation created/updated for this project, if necessary
• Documentation reviewed by technical writer or follow-up review issue created
• Tests added for this feature/bug
• Job definition updated, if necessary
  • Auto-DevOps template
  • Job definition example
  • CI Templates
• Conforms to the code review guidelines
• Conforms to the Go guidelines
• Security reports checked/validated by reviewer