support for histogram time series metric types

the `histogram` time series metric type is in [preview in 9.3](https://www.elastic.co/docs/manage-data/data-store/data-streams/time-series-data-stream-tsds#time-series-metric)

we should add it as allowed metric type [here](https://github.com/elastic/package-spec/blob/main/spec/integration/data_stream/fields/fields.spec.yml#L125) and add it to existing `histogram`/`exponential_histogram`/`tdigest`(?) field types e.g. [here](https://github.com/elastic/integrations/blob/main/packages/etcd/data_stream/metrics/fields/fields.yml#L42)