DBHeadline: add pulse alignment to match layout

[mriehl]

The DBHeadline currently offers a pulse attribute but this is always left-aligned below the heading.

However according to the DB Layout Guidelines (not sure if I can add a link here because it's on the extranet) the pulse alignment should follow the content alignment.
For example if the content is centered then the pulse needs to be centered below the heading too.

This could be achieved by adding a prop like pulseAlignment?: "start" | "center" | "end".

[mriehl]

Another solution could be to provide a standalone DBPulse component.