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/channel_view.go

@@ -0,0 +1,15 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package model
+
+type ChannelView struct {
+	ChannelId                 string `json:"channel_id"`
+	PrevChannelId             string `json:"prev_channel_id"`
+	CollapsedThreadsSupported bool   `json:"collapsed_threads_supported"`
+}
+
+type ChannelViewResponse struct {
+	Status            string           `json:"status"`
+	LastViewedAtTimes map[string]int64 `json:"last_viewed_at_times"`
+}