Investigate `x509_forced_cert_loading` feature flag

Problem

Feature flag x509_forced_cert_loading is disabled on GitLab.com.

It's not clear if the original problem still exists and if the fix is safe to apply.

Proposal

Review the original problem and try to test the fix behind the feature flag.

Possible outcomes:

• Proceed with a feature flag rollout
• Remove the feature flag and code behind it