Add annotations for certificates listed in /certs

Title: Add annotations for certificates listed in /certs

Description: Per discussion with @PiotrSikora and @incfly on https://github.com/envoyproxy/envoy/issues/7111#issuecomment-499291659, we need to add annotations or something similar into /certs dump to clearly display the type of each certificate, i.e., certificates from static secret, inline secret or SDS. It would be nice if we can add SDS resource name and other information into the annotation, so that we can associate certificates from /certs to SecretConfig(PR https://github.com/envoyproxy/envoy/pull/7365) dump from /config_dump while debugging SDS related issues.