TLS support for agentk observability endpoint
Closes gitlab-org/gitlab#375326 (closed).
Tested via local https://gdk.test:8080/metrics
with the following params: --observability-cert-file="/Users/mike/src/gdk/gdk.test.pem" --observability-key-file="/Users/mike/src/gdk/gdk.test-key.pem"
Edited by Mikhail Mazurskiy