Is there a way to use the alert manager to send an alert to external API,
I mean instead using excage server or slack etc, I will provide an endpoint
like https://mypullendpoint.host.com and the alert manager will send the
alert to this URL ?
The alert manager has a webhook config which allows you to send notifications on any HTTP(S) endpoint - provided the endpoint is ready to ingest the AM alerts in JSON format.
At this time there is no way to template the request so you need to have an integration somewhere.