[FEATURE] Uncertainty range examples

[nickhenden]

Preliminary Checks

• I have searched existing issues to ensure this feature hasn't been requested before

Proposed Solution

Add Matplotlib and Plotly example code for a line and/or bar chart with uncertainty ranges shown with shaded regions.

Examples:

• Line chart with uncertainty range (ONS)
• Bar chart with uncertainty range (ONS)

This would be needed for both Matplotlib and Plotly pages. If you are tackling just one of these, please create a specific sub-issue for Matplotlib/Plotly accordingly.