Update docs

Update docs for monitoring

ansible/docs/alertmanager.md

+### Alerting
+Configuration in values is set up for Slack and e-mail notifications. For Slack you need to get the [webhook](https://docs.kubermatic.com/kubermatic/v2.25/tutorials-howtos/monitoring-logging-alerting/user-cluster/setting-up-alertmanager-with-slack-notifications/#setting-up-slack-incoming-webhooks) URL and specify it under <code>.slack_configs.api_url</code>. For email alerts, provide the receiver's e-mail address, the SMTP server address and preferably configure a service account to act as the sender, then input these details in the relevant fields under  <code>.email_configs</code>.
+If you want to use different receiver refer to the [docs](https://prometheus.io/docs/alerting/latest/configuration/#general-receiver-related-settings).<br />
+To ignore specific alerts, add the alert name to <code>alertmanager.config.route.routes</code> under <code>receiver: 'null'</code>, and include it in the <code>alertname</code> field.
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