* [OPIK-884] experiment charts UI improvements

* [OPIK-884] update metric charts

* [OPIK-884] update copy

* [OPIK-884] show single dot if there is only one point with data

* [OPIK-884] show single dot for multiple lines

* [OPIK-884] fix lint

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Co-authored-by: Yaroslav Boiko <yaroslavboiko@ip-192-168-1-15.ec2.internal>