v8.0 module release (#22975)

https://mattermost.atlassian.net/browse/MM-52079

```release-note
We upgrade the module version to 8.0. The new module path is github.com/mattermost-server/server/v8.
```


Co-authored-by: Doug Lauder <wiggin77@warpmail.net>

server/model/post_embed.go

@@ -0,0 +1,25 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package model
+
+const (
+	PostEmbedImage             PostEmbedType = "image"
+	PostEmbedMessageAttachment PostEmbedType = "message_attachment"
+	PostEmbedOpengraph         PostEmbedType = "opengraph"
+	PostEmbedLink              PostEmbedType = "link"
+	PostEmbedPermalink         PostEmbedType = "permalink"
+	PostEmbedBoards            PostEmbedType = "boards"
+)
+
+type PostEmbedType string
+
+type PostEmbed struct {
+	Type PostEmbedType `json:"type"`
+
+	// The URL of the embedded content. Used for image and OpenGraph embeds.
+	URL string `json:"url,omitempty"`
+
+	// Any additional data for the embedded content. Only used for OpenGraph embeds.
+	Data any `json:"data,omitempty"`
+}