Feat/step function auto period

[dbuezas]

Example:

type: custom:plotly-graph
entities:
  - entity: sensor.temperature
    statistic: mean
    period:
      0: 5minute
      24h: hour # when the visible range is ≥ 1 day, use the `hour` period
      7d: day # from 7 days on, use `day`
      # 6M: week # not yet supported in HA
      1y: month # from 1 year on, use `month