Unstable metrics tracking due to conflicting dict key

In https://github.com/evo-company/hiku/blob/a7eca38095e24062dfdf1fc6c5e5666f25bf5144/hiku/telemetry/prometheus.py#L145 a `Link` function is used to aggregate fields during metrics collection. The problem  arrises when two links use same resolver function and both links are requested in the same query