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/channels/app/featureflag/feature_flags_sync.go

@@ -13,8 +13,8 @@ import (
 	"github.com/splitio/go-client/v6/splitio/client"
 	"github.com/splitio/go-client/v6/splitio/conf"
 
-	"github.com/mattermost/mattermost-server/v6/model"
-	"github.com/mattermost/mattermost-server/v6/server/platform/shared/mlog"
+	"github.com/mattermost/mattermost-server/server/v8/model"
+	"github.com/mattermost/mattermost-server/server/v8/platform/shared/mlog"
 )
 
 type SyncParams struct {

server/channels/app/featureflag/feature_flags_sync_test.go

@@ -8,7 +8,7 @@ import (
 
 	"github.com/stretchr/testify/require"
 
-	"github.com/mattermost/mattermost-server/v6/model"
+	"github.com/mattermost/mattermost-server/server/v8/model"
 )
 
 func TestGetStructFields(t *testing.T) {

server/channels/app/featureflag/split_logger.go

@@ -6,7 +6,7 @@ package featureflag
 import (
 	"fmt"
 
-	"github.com/mattermost/mattermost-server/v6/server/platform/shared/mlog"
+	"github.com/mattermost/mattermost-server/server/v8/platform/shared/mlog"
 )
 
 type splitLogger struct {