extra field require

**Is your feature request related to a problem? Please describe.**

in some case, I want to store some business key in one point data, as I know, no framework has implement include influxdb, openTSDB and so on, but I found [nightingale](https://github.com/didi/nightingale) support **extra** field in [this api](https://n9e.didiyun.com/docs/api/data/)

Start by reviewing the requested extra field and the linked Nightingale data API, then inspect the repository's data-ingestion and point representation areas. Clarify how a business key should be represented, accepted, stored, and returned, and define tests that demonstrate the expected behavior before implementation.

Written by the indexing model from the issue text.