Stop using self-signed certs during agent registration

Bug report:

Stork agent fails to start after upgrading to 1.12. It was working on the previous version. The logs contain the below message:

Aug 30 20:00:43 user (...) time="2023-08-30 20:00:43" level="error" msg="problem registering machine: problem sending POST to https://host/api/machines: Post \"https://host/api/machines\": x509: certificate signed by unknown authority" file="         register.go:383  "