Update _alertmanager-config.rst

[alifiroozi80]

the send_resolved is going to fail.

Error from server (BadRequest): error when creating "robusta-alert-config.yaml": AlertmanagerConfig in version "v1alpha1" cannot be handled as a AlertmanagerConfig: strict decoding error: unknown field "spec.receivers[0].webhookConfigs[0].send_resolved"

It should be sendResolved

---

$ k explain alertmanagerconfig.spec.receivers.webhookConfigs
GROUP:      monitoring.coreos.com
KIND:       AlertmanagerConfig
VERSION:    v1alpha1

FIELD: webhookConfigs <[]Object>

DESCRIPTION:
    List of webhook configurations.
    WebhookConfig configures notifications via a generic receiver supporting the
    webhook payload. See
    https://prometheus.io/docs/alerting/latest/configuration/#webhook_config
    
FIELDS:
  httpConfig	<Object>
    HTTP client configuration.

  maxAlerts	<integer>
    Maximum number of alerts to be sent per webhook message. When 0, all alerts
    are included.

  sendResolved	<boolean>
    Whether or not to notify about resolved alerts.

  url	<string>
    The URL to send HTTP POST requests to. `urlSecret` takes precedence over
    `url`. One of `urlSecret` and `url` should be defined.

  urlSecret	<Object>
    The secret's key that contains the webhook URL to send HTTP requests to.
    `urlSecret` takes precedence over `url`. One of `urlSecret` and `url` should
    be defined. The secret needs to be in the same namespace as the
    AlertmanagerConfig object and accessible by the Prometheus Operator.

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[arikalon1]

nice catch @alifiroozi80
Thanks for your contribution

[alifiroozi80]

My pleasure @arikalon1🍻