DER encoded certificates are not symlinked

Summary

Per our instructions on adding custom certificate authorities we included that DER or PEM encoded files work. After adding a certificate .der (also tested .cer, .crt) and reconfiguring the certificate is skipped and not symlinked.

# Docs
Note: The certificate must be either DER- or PEM-encoded.

# Reconfigure output
Skipping /etc/gitlab/trusted-certs/test_ca.der.

Steps to reproduce

Generate a der encoded certificate
Place into /etc/gitlab/trusted-certs
Reconfigure

Reproduced on 11.0.4 (reported on 10.7.5)

What is the current bug behavior?

Nothing symlinked/certificate is ignored

What is the expected correct behavior?

Symlink the certificate

Possible fixes

As a workaround, the same der can be converted to pem and afterward can be successfully symlinked.

openssl x509 -outform der -in root_ca.cer -out root_ca.pem

Internal ZD: https://gitlab.zendesk.com/agent/tickets/100436