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/user_autocomplete.go

@@ -0,0 +1,18 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package model
+
+type UserAutocompleteInChannel struct {
+	InChannel    []*User `json:"in_channel"`
+	OutOfChannel []*User `json:"out_of_channel"`
+}
+
+type UserAutocompleteInTeam struct {
+	InTeam []*User `json:"in_team"`
+}
+
+type UserAutocomplete struct {
+	Users        []*User `json:"users"`
+	OutOfChannel []*User `json:"out_of_channel,omitempty"`
+}