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

[tvalentyn]

What would you like to happen?

See Top.Of implementation that supports the key :

beam/sdks/python/apache_beam/transforms/combiners.py

Lines 212 to 213 in 7555d98

	key: (optional) a mapping of elements to a comparable key, similar to
	the key argument of Python's sorting methods.

Let's allow the same for

Top.Smallest / Largest and the ...PerKey combiners, see:

beam/sdks/python/apache_beam/transforms/combiners.py

Line 296 in 7555d98

def Largest(pcoll, n, has_defaults=True):

Issue Priority

Priority: 3 (nice-to-have improvement)

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[tvalentyn]

cc: @harrisonlimh

[harrisonlimh]

.take-issue