Allow non-integral values for kafka_span_sample_rate_percent

[ChimeraCoder]

Summary

Allow non-integer values for the Kafka sample rate. This allows us to sample at rates less than 1% (or rates in between integer values).

Motivation

Test plan

Rollout/monitoring/revert plan

r? @joshu-stripe cc @stripe/observability

[stripe-ci]

Gerald Rule: Copy Observability on Veneur and Unilog pull requests

cc @stripe/observability cc @stripe/observability-stripe

[ChimeraCoder]

Joshu is OOO this week

r? @cory-stripe

[cory-stripe]

👍

From looking at the code it doesn't care of it's a float or not once the signature was fixed. Assuming tests pass looks great!