Configurable update interval on picture-element

[coreGreenberet]

At the moment the picture element will update it's picture every 10 seconds.
This interval is sadly to high for elements which are having a live stream (e.g. security camera) and not all devices (E.g. chromecast) are supporting the live stream of the element.
Therefore it would be nice to have a configurable update interval on the lovelace card