Change timestamp format used in gateway API

[benfrancis]

Timestamps for actions and events in the gateway API are currently in the format 2022-01-20T17:21:12+00:00.

The latest draft of the W3C WoT Profile specification constrains the date format so that it must end in "Z".

If and when w3c/wot-profile#119 and w3c/wot-profile#127 land, I suggest changing action.ts and event.ts to use Date().toISOString() directly rather than Utils.timestamp(), which should output the expected date format.

See WebThingsIO/gateway-addon-node#106 for more information.

[adioanca]

Hi,
Both 119 and 127 were closed this year. Think it would be a good idea to move to .123 milisecond Z format.

(see my other comment in WebThingsIO/gateway-addon-node#106

[benfrancis]

I agree.

See also: WebThingsIO/gateway-addon-node#106 (comment)

[benfrancis]

The latest draft of WoT Profile only requires that timestamps conform to RFC3339, which does allow both numerical timezone offsets and "Z". As I understand it that means the timestamps used by the gateway do now comply with the specification.

However, I think we should still change the gateway to use Date().toISOString() directly to allow millisecond precision timestamps.