text: Title: Make Panel Extensions visible
  Body: Now that Panel extensions start to pop up I believe we should maintain a list somewhere. I thought about `panel-extensions` org. But that is not visible enough.
  
  I think we should have a page similar to our Panel Components page or integrated with the Panel Components page (like Streamlit does).
  
  At first we could just list, describe and link to them. Later we could add thumbnails if we believe it creates value.
  
  ----
  
  ```markdown
  ## 📚 Discover Extensions
  
  Here we maintain a list of Panel Extensions maintained inside and outside this organisation.
  
  ### Widgets
  
  #### [`panel-material-ui`](https://github.com/panel-extensions/panel-material-ui)
  
  An extension to bring MaterialUI components to Panel.
  
  ### Visualizations
  
  #### [`panel-graphic-walker`](https://github.com/panel-extensions/panel-graphic-walker)
  
  A Tableau like *Graphic Walker* pane for use with HoloViz Panel.
  
  ### Jupyter Extensions
  
  #### [`jupyter_bokeh`](https://github.com/bokeh/jupyter_bokeh)
  
  A Jupyter extension for rendering Bokeh and Panel content within Jupyter environments.
  
  #### [`ipywidgets_bokeh`](https://github.com/bokeh/ipywidgets_bokeh)
  
  Support for using Ipywidgets within Bokeh and Panel.
  
  ### Templates
  
  ```