* Pass prometheus registerer to the dual writer
* Fix tests
* Remove unused var
* Fix tests
* Uncomment test
* Remove leading line
* Fix tests. Reuse registerer if there's already one
* Lint
* Improve double registering logic
* Rebase main
* Add feature toggles for mode 2 and 3 playlist dual writing
* Make current mode customised based on kind
* Check feature flags when initialising dual writer
* Fix linting
* Refactor NewDualWriter