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/boards/services/webhook/webhook.go

@@ -9,10 +9,10 @@ import (
 	"io"
 	"net/http"
 
-	"github.com/mattermost/mattermost-server/v6/server/boards/model"
-	"github.com/mattermost/mattermost-server/v6/server/boards/services/config"
+	"github.com/mattermost/mattermost-server/server/v8/boards/model"
+	"github.com/mattermost/mattermost-server/server/v8/boards/services/config"
 
-	"github.com/mattermost/mattermost-server/v6/server/platform/shared/mlog"
+	"github.com/mattermost/mattermost-server/server/v8/platform/shared/mlog"
 )
 
 // NotifyUpdate calls webhooks.

server/boards/services/webhook/webhook_test.go

@@ -10,10 +10,10 @@ import (
 
 	"github.com/stretchr/testify/assert"
 
-	"github.com/mattermost/mattermost-server/v6/server/boards/model"
-	"github.com/mattermost/mattermost-server/v6/server/boards/services/config"
+	"github.com/mattermost/mattermost-server/server/v8/boards/model"
+	"github.com/mattermost/mattermost-server/server/v8/boards/services/config"
 
-	"github.com/mattermost/mattermost-server/v6/server/platform/shared/mlog"
+	"github.com/mattermost/mattermost-server/server/v8/platform/shared/mlog"
 )
 
 func TestClientUpdateNotify(t *testing.T) {