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_count.go

@@ -0,0 +1,42 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package model
+
+import (
+	"crypto/md5"
+	"fmt"
+	"sort"
+	"strconv"
+)
+
+type ChannelCounts struct {
+	Counts      map[string]int64 `json:"counts"`
+	CountsRoot  map[string]int64 `json:"counts_root"`
+	UpdateTimes map[string]int64 `json:"update_times"`
+}
+
+func (o *ChannelCounts) Etag() string {
+	// we don't include CountsRoot in ETag calculation, since it's a derivative
+	ids := []string{}
+	for id := range o.Counts {
+		ids = append(ids, id)
+	}
+	sort.Strings(ids)
+
+	str := ""
+	for _, id := range ids {
+		str += id + strconv.FormatInt(o.Counts[id], 10)
+	}
+
+	md5Counts := fmt.Sprintf("%x", md5.Sum([]byte(str)))
+
+	var update int64 = 0
+	for _, u := range o.UpdateTimes {
+		if u > update {
+			update = u
+		}
+	}
+
+	return Etag(md5Counts, update)
+}