Variable support_email in error_extra.html contains empty value

[michaelwood]

support_email appears to be correctly configured in COVE_CONFIG but the value does not appear to be passed back in the context.

https://github.com/OpenDataServices/lib-cove-web/blob/main/cove/templates/error_extra.html

Reproduce:

• Attempt to test a invalid json document.

Tested on oc4ids and threesixtygiving's cove.

[jpmckinney]

This issue is now closed @odscjames @Bjwebb