Sum aggregation function should support more types

[ernest-liftoff]

Component(s)

processor/metricstransform, processor/transform

Describe the issue you're reporting

NOTE: Only the sum aggregation function is supported for histogram and exponential histogram datatypes

This a new additional in processor/metricstransform, as it did not use to have this restriction. I understand that sum aggregation on sum types are incorrect, but that is only in the cumulative format. There should be no problem if the data is in the delta format.

Furthermore,  summing gauge (while it may or may not be correct), it should be allowed & up to user's discretion.

[github-actions]

Pinging code owners:

• processor/metricstransform: @dmitryax
• processor/transform: @TylerHelmuth @kentquirk @bogdandrutu @evan-bradley

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[ernest-liftoff]

sorry, misunderstood the statement