title: Python plotly legendgrouptitle_text is not working as go.Scatter argument
body: <p>I'm trying to use <code>legendgrouptitle_text</code> to set legendgroup title on python <code>go.Scatter</code> as mentionned in plotly doc:</p>
  <ul>
  <li><a href="https://plotly.com/python/legend/" rel="nofollow noreferrer">https://plotly.com/python/legend/</a></li>
  <li><a href="https://plotly.com/python/reference/scatterpolar/#scatterpolar-legendgrouptitle" rel="nofollow noreferrer">https://plotly.com/python/reference/scatterpolar/#scatterpolar-legendgrouptitle</a></li>
  </ul>
  <p>But go.Scatter refuses it as argument and suggest other inaproriate argument :</p>
  <pre><code>    Did you mean &quot;legendgroup&quot;?
  
      Bad property path:
  
      legendgrouptitle_text
      ^^^^^^^^^^^^^^^^
  </code></pre>
  <p>Here's a snippet code of how I try to use it</p>
  <pre><code>traces.append(
      go.Scatter(
          x=X_1d,
          y=y_1d,
          name=', '.join(features_values),
          showlegend=True,
          line=dict(
              color=color,
              dash='solid',
              width=2,
          ),
          marker=dict(
              color=color,
              symbol='circle',
              size=marker_size,
          ),
          opacity=opacity,
          legendgroup='fixed_features',
          legendgrouptitle_text='[' + ', '.join(legend_features) + ']',
      )
  )
  </code></pre>
  <p>Many thanks in advance !</p>