[Feature Request]: Top.Smallest / Largest and the ...PerKey helper combiners should support a comparison key param

### What would you like to happen?

See Top.Of implementation that supports the `key` : https://github.com/apache/beam/blob/7555d9897996362a82e6e5d25202ddf29931338d/sdks/python/apache_beam/transforms/combiners.py#L212-L213

Let's allow the same for

Top.Smallest / Largest and the ...PerKey combiners, see: https://github.com/apache/beam/blob/7555d9897996362a82e6e5d25202ddf29931338d/sdks/python/apache_beam/transforms/combiners.py#L296

### Issue Priority

Priority: 3 (nice-to-have improvement)

### Issue Components

- [X] Component: Python SDK
- [ ] Component: Java SDK
- [ ] Component: Go SDK
- [ ] Component: Typescript SDK
- [ ] Component: IO connector
- [ ] Component: Beam examples
- [ ] Component: Beam playground
- [ ] Component: Beam katas
- [ ] Component: Website
- [ ] Component: Spark Runner
- [ ] Component: Flink Runner
- [ ] Component: Samza Runner
- [ ] Component: Twister2 Runner
- [ ] Component: Hazelcast Jet Runner
- [ ] Component: Google Cloud Dataflow Runner