Prompt differently for new skills tracked vs onboarding

[boazsender]

In #87 we made the "skills" missing work better in the context of new skills being added to track.

Consider branching this logic to give different prompts for when the org starts tracking a new skill versus, a new team member filling this out for the first time. Eg:

we're tracking n new skills this week

[tkellen]

As a note, the heuristic we'd use for this would be if the person receiving the message has no skill values logged at all.