API can use mixed inhibition rules during a configuration reload #5593

During a configuration reload, Alertmanager updates the API before it publishes the new inhibitor.

For a short time, an API request can use the new configuration with the old inhibitor. A request that started before the reload can also use the old API callback with the new inhibitor.

This can make the API report an incorrect inhibited or active status for an alert while the reload is in progress.

Expected behavior: Each API request uses inhibition rules from one complete configuration: either the old configuration or the new configuration.

Actual behavior: A request can use parts of both configurations.