PNET-364 Add content to SAFe for SKA page.

As Nick suggested some time ago, the SAFe for SKA confluence page should migrate to the developer portal, so we have a place to point contractors who need to understand how this works for SKA.

I was hoping to add a picture to show the 'heartbeat' of the cadence of meetings, but I haven't yet got a png or jpeg for a good image. I don't think this should block a merge.

I don't believe there are any licensing issues regarding the discussion of SAFe and the use of SAFe terminology, but I'd appreciate a second opinion on this.