title: Seaborn Lineplot show custom central line instead of mean
body: <p>I have a dataset that is consisting of three values for each timestep: Once the mean value as well as the lower and upper error bound.</p>
  
  <pre><code>name,year,area
  test,2017,1.0376800009967053 #mean
  test,2017,0.09936810445983806 #lower bound
  test,2017,2.118230806622908 #upper bound and so on ...
  test,2018,1.0
  test,2018,0.13705391957353763
  test,2018,2.1881023056535183
  test,2019,1.2928531655977922
  test,2019,0.17400072775054737
  test,2019,3.016064939443665
  </code></pre>
  
  <p>I would like to plot the data so that I get a shaded area between the upper and the lower bound and have a line in between that follows the mean value in the dataset. </p>
  
  <p>I have tried seaborn.lineplot
  (<a href="https://seaborn.pydata.org/examples/errorband_lineplots.html" rel="nofollow noreferrer">https://seaborn.pydata.org/examples/errorband_lineplots.html</a>)
  however it calculates the mean of the tree values and so the line is not where the actual mean should be.
  Any body got some ideas?
  Is it possible to change the way seaborn calculates the central line? (for example to median)</p>