alertmanager

[roidelapluie]

A lot of alertmanager users are experiencing issues due to mismatch between alertmanager and amtool.

prometheus/alertmanager#2672 introduces a way of detecting this, but some third party tools like cortex do not reply with the alertmanager version when queried on the alertmanager version endpoint, instead pointing to their own version.

We should, in the alertmanager compliance, state that the version endpoint must return the alertmanager release.