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/platform/services/imageproxy/atmos_camo_test.go

@@ -13,9 +13,9 @@ import (
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 
-	"github.com/mattermost/mattermost-server/v6/model"
-	"github.com/mattermost/mattermost-server/v6/server/channels/utils/testutils"
-	"github.com/mattermost/mattermost-server/v6/server/platform/services/httpservice"
+	"github.com/mattermost/mattermost-server/server/v8/channels/utils/testutils"
+	"github.com/mattermost/mattermost-server/server/v8/model"
+	"github.com/mattermost/mattermost-server/server/v8/platform/services/httpservice"
 )
 
 func makeTestAtmosCamoProxy() *ImageProxy {

server/platform/services/imageproxy/imageproxy.go

@@ -11,10 +11,10 @@ import (
 	"strings"
 	"sync"
 
-	"github.com/mattermost/mattermost-server/v6/model"
-	"github.com/mattermost/mattermost-server/v6/server/platform/services/configservice"
-	"github.com/mattermost/mattermost-server/v6/server/platform/services/httpservice"
-	"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/services/configservice"
+	"github.com/mattermost/mattermost-server/server/v8/platform/services/httpservice"
+	"github.com/mattermost/mattermost-server/server/v8/platform/shared/mlog"
 )
 
 var ErrNotEnabled = Error{errors.New("imageproxy.ImageProxy: image proxy not enabled")}

server/platform/services/imageproxy/local.go

@@ -19,7 +19,7 @@ import (
 	"strings"
 	"time"
 
-	"github.com/mattermost/mattermost-server/v6/server/platform/shared/mlog"
+	"github.com/mattermost/mattermost-server/server/v8/platform/shared/mlog"
 )
 
 var imageContentTypes = []string{

server/platform/services/imageproxy/local_test.go

@@ -13,9 +13,9 @@ import (
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 
-	"github.com/mattermost/mattermost-server/v6/model"
-	"github.com/mattermost/mattermost-server/v6/server/channels/utils/testutils"
-	"github.com/mattermost/mattermost-server/v6/server/platform/services/httpservice"
+	"github.com/mattermost/mattermost-server/server/v8/channels/utils/testutils"
+	"github.com/mattermost/mattermost-server/server/v8/model"
+	"github.com/mattermost/mattermost-server/server/v8/platform/services/httpservice"
 )
 
 func makeTestLocalProxy() *ImageProxy {