Alerting: Add Documentation about limits of images in notifications. (#51084)

Because some contact points only support a single image, and the order
of alerts sent to a contact point is not guaranteed, which alert rule's
image is attached to a notification can change from alert to alert. This
documents that behavior.

docs/sources/alerting/images-in-notifications.md

@@ -20,9 +20,9 @@ If Grafana is set up to send images in notifications, it takes a screenshot of t
 1. The alert rule transitions from pending to firing
 2. The alert rule transitions from firing to OK
 
-Images are stored in the [data]({{< relref "../setup-grafana/configure-grafana/#paths" >}}) path and so Grafana must have write-access to this path. If Grafana cannot write to this path then taken screenshots cannot be saved to disk and an error will be logged for each failed screenshot attempt. In addition to storing images on disk, Grafana can also store the image in an external image store such as Amazon S3, Azure Blob Storage, Google Cloud Storage and even Grafana where screenshots are stored in `public/img/attachments`. Screenshots older than `temp_data_lifetime` are deleted from disk but not the external image store. If Grafana is the external image store then screenshots are deleted from `data` but not from `public/img/attachments`.
+Images are stored in the [data]({{< relref "../setup-grafana/configure-grafana/#paths" >}}) path and so Grafana must have write-access to this path. If Grafana cannot write to this path then screenshots cannot be saved to disk and an error will be logged for each failed screenshot attempt. In addition to storing images on disk, Grafana can also store the image in an external image store such as Amazon S3, Azure Blob Storage, Google Cloud Storage and even Grafana where screenshots are stored in `public/img/attachments`. Screenshots older than `temp_data_lifetime` are deleted from disk but not the external image store. If Grafana is the external image store then screenshots are deleted from `data` but not from `public/img/attachments`.
 
-> **Note**: It is recommended to use an external image store is used for images in notifications as not all contact points supported uploading images from disk. It is also possible that the image on disk is deleted before an alert notification is sent if `temp_data_lifetime` is less than the `group_wait` and `group_interval` options used in Alertmanager.
+> **Note**: It is recommended that you use an external image store, as not all contact points support uploading images from disk. It is also possible that the image on disk is deleted before an alert notification is sent if `temp_data_lifetime` is less than the `group_wait` and `group_interval` options used in Alertmanager.
 
 ## Requirements
 
@@ -92,3 +92,9 @@ For example, if a screenshot could not be taken within the expected time (10 sec
 - `grafana_screenshot_successes_total`
 - `grafana_screenshot_upload_failures_total`
 - `grafana_screenshot_upload_successes_total`
+
+## Limitations
+
+- Images in notifications are not available for Grafana Mimir and Loki managed alert rules, or when Grafana is set up to send alert notifications to an external Alertmanager.
+- When alerts generated by different alert rules are sent in a single notification, there may be screenshots for each alert rule. This happens if an alert group contains multiple alerting rules. The order the images are attached is random. If you need to guarantee the ordering of images, make sure that your alert groups contain a single alerting rule.
+- Some contact points only handle a single image. In this case, the first image associated with an alert will be attached. Because the ordering is random, this may not always be an image for the same alert rule. If you need to guarantee you receive a screenshot for a particular rule, make sure that your alert groups contain a single alerting rule.