Add block documentation for Slack (#12518)

* Add block documentation for Slack

* Code review

* Updates from code review

source/_integrations/slack.markdown

@@ -75,77 +75,65 @@ The following attributes can be placed inside `data` for extended functionality.
 
 | Service data attribute | Optional | Description |
 | ---------------------- | -------- | ----------- |
-| `file`                 |      yes | Groups the attributes for file upload. If present, either `url` or `path` have to be provided.
-| `path `                |      yes | Local path of file, photo etc to post to Slack. Is placed inside `file`.
-| `url`                  |      yes | URL of file, photo etc to post to Slack. Is placed inside `file`.
-| `username`             |      yes | Username if the URL requires authentication. Is placed inside `file`.
-| `password`             |      yes | Password if the URL requires authentication. Is placed inside `file`.
-| `auth`                 |      yes | If set to `digest` HTTP-Digest-Authentication is used. If missing HTTP-BASIC-Authentication is used. Is placed inside `file`.
-| `attachments`          |      yes | Array of [Slack attachments](https://api.slack.com/docs/message-attachments). See [the attachment documentation](https://api.slack.com/docs/message-attachments) for how to format. *NOTE*: if using `attachments`, they are shown **in addition** to `message`
+| `file`                   |      yes | Local path of file, photo, etc. to post to Slack.
+| `attachments`            |      yes | Array of [Slack attachments](https://api.slack.com/messaging/composing/layouts#attachments) (legacy). *NOTE*: if using `attachments`, they are shown **in addition** to `message`.
+| `blocks`                 |      yes | Array of [Slack blocks](https://api.slack.com/messaging/composing/layouts). *NOTE*: if using `blocks`, they are shown **in addition** to `message`.
 
-Example for posting file from URL:
+Example for posting a file from local path:
 
-```json
-{
-  "message":"Message that will be added as a comment to the file.",
-  "title":"Title of the file.",
-  "target": ["#channelname"], 
-  "data":{
-    "file":{
-      "url":"http://[url to file, photo, security camera etc]",
-      "username":"optional user, if necessary",
-      "password":"optional password, if necessary",
-      "auth":"digest"
-    }
-  }
-}
+```yaml
+message: Message that will be added as a comment to the file.
+title: Title of the file.
+data:
+  file: "/path/to/file.ext"
 ```
 
-Example for posting file from local path:
+Please note that `file` is validated against the `whitelist_external_dirs` in the `configuration.yaml`.
 
-```json
-{
-  "message":"Message that will be added as a comment to the file.",
-  "title":"Title of the file.",
-  "data":{
-    "file":{
-      "path":"/path/to/file.ext"
-    }
-  }
-}
+Example for using the block framework:
+
+```yaml
+message: Message that will be added as a comment to the file.
+title: Title of the file.
+data:
+  attachments:
+    - type: section
+      text:
+        type: mrkdwn
+        text: 'Danny Torrence left the following review for your property:'
+    - type: section
+      block_id: section567
+      text:
+        type: mrkdwn
+        text: "<https://example.com|Overlook Hotel> \n :star: \n Doors had too many
+          axe holes, guest in room 237 was far too rowdy, whole place felt stuck in
+          the 1920s."
+      accessory:
+        type: image
+        image_url: https://is5-ssl.mzstatic.com/image/thumb/Purple3/v4/d3/72/5c/d3725c8f-c642-5d69-1904-aa36e4297885/source/256x256bb.jpg
+        alt_text: Haunted hotel image
+    - type: section
+      block_id: section789
+      fields:
+      - type: mrkdwn
+        text: |-
+          *Average Rating*
+          1.0
 ```
 
-Please note that `path` is validated against the `whitelist_external_dirs` in the `configuration.yaml`.
+Example for using the legacy attachments framework:
 
-Example for posting formatted attachment:
-
-```json
-{
-  "message": "",
-  "data": {
-    "attachments": [
-      {
-        "title": "WHAT A HORRIBLE NIGHT TO HAVE A CURSE.",
-        "image_url": "https://i.imgur.com/JEExnsI.gif"
-      }
-    ]
-  }
-}
+```yaml
+message: Message that will be added as a comment to the file.
+title: Title of the file.
+data:
+  attachments:
+    - title: WHAT A HORRIBLE NIGHT TO HAVE A CURSE.
+      image_url: https://i.imgur.com/JEExnsI.gif
 ```
 
 You can also use YAML to send messages from your automations
 
-```yaml
-
-    - service: notify.slack
-      data:
-        message: "Latest notification"
-        title: "Latest image"
-        target: ["#home-assistant"]
-        data:
-          file:
-            path: "/myfile.jpg"
-```
 Please note that both `message` is a required key, but is always shown, so use an empty (`""`) string for `message` if you don't want the extra text.
 
 To use notifications, please see the [getting started with automation page](/getting-started/automation/).