title: Adding dates into a hovertemplate plotly
body: <p>I am very new to plotly and have run into some trouble formatting the hover info. I am trying to use the <code>hovertemplate</code> in order to provide specific text that I want, as opposed to whatever the graph auto formats to. I want to supply a list of dates, as well as a value and some additional text. However, when trying to supply a date it does not seem to format. I tried doing an exact example from plotly documentation that I will show below.</p>
  <pre class="lang-py prettyprint-override"><code>import plotly.graph_objs as go
  
  fig = go.Figure()
  fig.add_trace(
      go.Scatter(x=dict2['time'],
                 y=dict2['2m_temp_prod'],
                 mode='markers+lines',
                 name='Sfc Temp',
                 line=dict(color='red', width=4),
                 hovertemplate='Day: %{2019-01-01|%A}'))
  </code></pre>
  <p>The hover text does not properly convert the date and instead reads Day: %{2019-01-01|%A}. Any ideas on how to fix this?</p>
  <p>Edit: Here is a more workable example.</p>
  <p>I load in some data from an xarray dataarray and transform it into a dictionary.</p>
  <pre><code>dict2
  
  {'time': 0    2020-08-12 00:00:00
   1    2020-08-12 06:00:00
   2    2020-08-12 12:00:00
   3    2020-08-12 18:00:00
   4    2020-08-13 00:00:00
                ...        
   56   2020-08-26 00:00:00
   57   2020-08-26 06:00:00
   58   2020-08-26 12:00:00
   59   2020-08-26 18:00:00
   60   2020-08-27 00:00:00
   Name: time, Length: 61, dtype: datetime64[ns],
   '2m_temp_prod': 0     84.0
   1     74.0
   2     71.0
   3     82.0
   4     79.0
         ... 
   56    79.0
   57    70.0
   58    67.0
   59    82.0
   60    80.0
   Name: 2m_temp_prod, Length: 61, dtype: float64,
   '2m_temp_area': 0     84.0
   1     74.0
   2     70.0
   3     82.0
   4     80.0
         ... 
   56    79.0
   57    70.0
   58    67.0
   59    82.0
   60    80.0
   Name: 2m_temp_area, Length: 61, dtype: float64}
  </code></pre>
  <p>This data plots fine as a line plot, but the hovertext is wrong, as described above. I tried just copying the example date from the plotly documentation above, but ultimately I want to provide a list of string dates to be applied to the hovertext instead of the autogenerated hovertext. I would like the hovertext to say: Day: Tuesday. The code is supposed to take the date and only output the day of the week. In this case, Jan 1, 2019 was on a Tuesday. Plot for reference.</p>
  <p><a href="https://i.stack.imgur.com/fuAkW.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/fuAkW.png" alt="enter image description here" /></a></p>