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/plugin/context.go

@@ -0,0 +1,15 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package plugin
+
+// Context passes through metadata about the request or hook event.
+// For requests this is built in app/plugin_requests.go
+// For hooks, app.PluginContext() is called.
+type Context struct {
+	SessionId      string
+	RequestId      string
+	IPAddress      string
+	AcceptLanguage string
+	UserAgent      string
+}