text: Title: Allow applying patterns to single values
  Body: Context: plotly.express.timeline
  
  Looking at (and neighboring lines which perform analogous checks) https://github.com/plotly/plotly.py/blob/216fca2a7ed14d2e58f5423557b6e731e2a0f575/packages/python/plotly/plotly/express/_core.py#L973, there is no way to set `pattern_shape_sequence` to `['']` and set patterns for individual values within `pattern_shape_map`. All I want is to make one specific thing stand out without changing its color.
  
  …unless there is another way to achieve that that I’d missed.
  