Refactor of /bridges API to make it more consistent with other APIs:
- bridge enable/disable is now done via the endpoint `/bridges/{id}/enable/[true,false]`
- `/bridges/{id}/operation/{operation}` endpoints are now `/bridges/{id}/{operation}`
- metrics are moved out from the GET `/bridges/{id}` response and can now be fetched via `/bridges/{id}/metrics`
- the `bridges/{id}/reset_metrics` endpoint is now `/bridges/{id}/metrics/reset`