Merge branch 'docs-oidc-aws-troubleshooting' into 'master'

Add error to troubleshooting when there's certificate chain issue

See merge request https://gitlab.com/gitlab-org/gitlab/-/merge_requests/143600



Merged-by: Marcel Amirault <mamirault@gitlab.com>
Approved-by: Marcel Amirault <mamirault@gitlab.com>
Reviewed-by: Marcel Amirault <mamirault@gitlab.com>
Co-authored-by: Elif Munn <emunn@gitlab.com>