MM-36271: Bump major version to 6.0 (#17973)

https://mattermost.atlassian.net/browse/MM-36271

```release-note
We bump the major version to 6.0
```

services/tracing/tracing.go

@@ -14,7 +14,7 @@ import (
 	"github.com/uber/jaeger-client-go/zipkin"
 	"github.com/uber/jaeger-lib/metrics"
 
-	"github.com/mattermost/mattermost-server/v5/shared/mlog"
+	"github.com/mattermost/mattermost-server/v6/shared/mlog"
 )
 
 // Tracer is a wrapper around Jaeger OpenTracing client, used to properly de-initialize jaeger on exit