FetchNamespaceFromContext if not found, fallback to default.

NamespaceUnaryInterceptor namespace can be passed in jwt token or headers, if none provided it falls back to default.

UserHeaderCtx middleware will propagate a valid user ID as string within request context use `user.FromContext` function to get the user ID string.

NamespaceKey is injected in context with the tenant context.

go:generate mockery --name=StatsDClient -r --case underscore --with-expecter --structname StatsDClient --filename statsd_monitor.go --output=./mocks.