Add "Last updated" to charts

**Is your feature request related to a problem? Please describe.**
User does not know how fresh the data is or how often the data is updated. This is particularly an issue since most of our data is only updated monthly, quarterly, or some even yearly. We need to provide a reason why the data may be "stale".

Additionally, admin should be able to see when charts are about to be updated, so that content can be prepared in advance.

**Describe the solution you'd like**
On the charts, on the footer, next to Source and Target, add "Updated: " to show when the data was last updated by the data source. This is the date that the data was last updated in the source. I.e. in Statcan tables, this is the "Release date"

**Describe alternatives you've considered**
N/A

**Additional context**
N/A