stats: Add chart metadata to the `/lines/<chart_id>` endpoint

[isstuev]

Product task https://github.com/blockscout/frontend/issues/1966

Currently we receive chart's title, description and units only from the /lines endpoint We're implementing a separate chart page and don't want to fetch data of all charts, so it seems reasonable to move all the metadata to the particular chart's endpoint and keep only charts ids in the /lines response