Upgrade to npm 6.14.8, musl 1.1.20-r5

What does this MR do?

• Add apk upgrade command to Dockerfile to ensure that all installed packages are recent
• Upgrade to npm 6.14.8, musl 1.1.20-r5, musl-utils 1.1.20-r5, libcrypto1.1 1.1.1g-r0, libssl1.1 1.1.1g-r0, and ca-certificates-cacert 20191127-r2
• Remove yarn 1.15.2, which was not used

What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab/-/issues/247080

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