alerting docs: update slack integration

A request was made for full documentation of the Slack app and its configuration options. This PR updates the documentation page with full app configuration documented.

docs/sources/alerting/configure-notifications/manage-contact-points/integrations/configure-slack.md

@@ -43,7 +43,7 @@ There are two ways of integrating Slack into Grafana Alerting.
 
 Note that you can only setup one Slack channel per contact point.
 
-You can customize the `title` and `body` of the Slack message using [notification templates](ref:notification-templates); however, you cannot modify its visual appearance with custom blocks.
+You can customize the `title` and `body` of the Slack message using [notification templates](ref:notification-templates); however, you cannot modify its visual appearance with custom blocks. Additional optional settings are available to customize bot appearance, mentions, and message formatting. Refer to the [Optional settings](#optional-settings) section for more details.
 
 ## Before you begin
 
@@ -83,6 +83,47 @@ To create your Slack integration in Grafana Alerting, complete the following ste
 
 1. Click **Save contact point**.
 
+## Optional settings
+
+You can configure additional settings to customize your Slack notifications beyond the required fields.
+
+### Customize bot appearance
+
+You can customize how the bot appears in Slack channels:
+
+- **Username**: Override the default bot username that appears in Slack. Set the `username` field to customize the display name.
+- **Icon emoji**: Provide an emoji to use as the icon for the bot's message. Set the `icon_emoji` field (for example, `:rocket:`). This overrides the icon URL.
+- **Icon URL**: Provide a URL to an image to use as the icon for the bot's message. Set the `icon_url` field with the image URL.
+
+### Configure mentions
+
+You can automatically mention users, groups, or the entire channel when notifications are sent:
+
+- **Mention users**: Mention one or more specific users in the notification. Set the `mentionUsers` field with a comma-separated list of user IDs (for example, `U024BE7LH,U024BE7LJ`). To find a user's ID, refer to [Slack's documentation on finding member IDs](https://api.slack.com/methods/users.list).
+
+- **Mention groups**: Mention one or more user groups in the notification. Set the `mentionGroups` field with a comma-separated list of group IDs. You can copy group IDs from the group's Slack profile URL.
+
+- **Mention channel**: Mention the entire channel or active members. Set the `mentionChannel` field to one of the following:
+  - Empty or omit the field to disable channel mentions
+  - `here` to mention every active channel member
+  - `channel` to mention every channel member
+
+### Customize message content
+
+You can customize the notification message using [notification templates](ref:notification-templates):
+
+- **Title**: Set a custom title for the Slack message. Use the `title` field with template variables (for example, `{{ template "slack.default.title" . }}`).
+
+- **Text body**: Set a custom body text for the Slack message. Use the `text` field with template variables (for example, `{{ template "slack.default.text" . }}`).
+
+- **Color**: Set the color of the vertical bar on the left side of the message attachment. Use the `color` field with either:
+
+### Advanced configuration
+
+For specialized environments, you can override the default Slack API endpoint:
+
+- **Endpoint URL**: Specify a custom Slack API endpoint for non-webhook requests. Set the `endpointUrl` field to your custom endpoint. The default is `https://slack.com/api/chat.postMessage`. 
+
 ## Next steps
 
 The Slack contact point is ready to receive alert notifications.