Automate datasource catalog check and show in frontend

[ots22]

Extends #566:

• modifies the script to emit javascript that can be loaded by the frontend
• runs the check on a schedule and stores the output as an artifact
• load and show the result in the frontend (see below)

[IFenton]

That all looks fine to me (though you could make the validation date value on the website slightly less precise)

[ots22]

That all looks fine to me (though you could make the validation date value on the website slightly less precise)

Date now visible on hover over the 'validation check' heading (now in RFC 7231 format, with seconds but no milliseconds)