MM-53032: Fix module path after repo rename (#23689)

It was a good decision in hindsight to keep the public module as 0.x
because this would have been a breaking change again.

https://mattermost.atlassian.net/browse/MM-53032
```release-note
Changed the Go module path from github.com/mattermost/mattermost-server/server/v8 to github.com/mattermost/mattermost/server/v8.

For the public facing module, it's path is also changed from github.com/mattermost/mattermost-server/server/public to github.com/mattermost/mattermost/server/public
```

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/server/public/model"
-	"github.com/mattermost/mattermost-server/server/v8/channels/utils/testutils"
-	"github.com/mattermost/mattermost-server/server/v8/platform/services/httpservice"
+	"github.com/mattermost/mattermost/server/public/model"
+	"github.com/mattermost/mattermost/server/v8/channels/utils/testutils"
+	"github.com/mattermost/mattermost/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/server/public/model"
-	"github.com/mattermost/mattermost-server/server/public/shared/mlog"
-	"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/public/model"
+	"github.com/mattermost/mattermost/server/public/shared/mlog"
+	"github.com/mattermost/mattermost/server/v8/platform/services/configservice"
+	"github.com/mattermost/mattermost/server/v8/platform/services/httpservice"
 )
 
 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/server/public/shared/mlog"
+	"github.com/mattermost/mattermost/server/public/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/server/public/model"
-	"github.com/mattermost/mattermost-server/server/v8/channels/utils/testutils"
-	"github.com/mattermost/mattermost-server/server/v8/platform/services/httpservice"
+	"github.com/mattermost/mattermost/server/public/model"
+	"github.com/mattermost/mattermost/server/v8/channels/utils/testutils"
+	"github.com/mattermost/mattermost/server/v8/platform/services/httpservice"
 )
 
 func makeTestLocalProxy() *ImageProxy {