* By default, get keys from keys.datadoghq.com, not Ubuntu keyserver
* Always add the DATADOG_APT_KEY_CURRENT.public key (contains key used to sign current repodata)
* Add 'signed-by' option to all sources list lines
* On Debian >= 9 and Ubuntu >= 16, only add keys to /usr/share/keyrings/datadog-archive-keyring.gpg
* On older systems, also add the same keyring to /etc/apt/trusted.gpg.d