[FEATURE]: `form_complete_pct` in supertibble

[rsh52]

Feature Request Description

Add an additional metadata column to the supertibble, form_complete_pct, showing the percentage of form_status_complete for each data tibble.

Checklist

• [x] The issue is atomic
• [x] The issue description is documented
• [x] The issue title describes the problem succinctly
• [x] Developers are assigned to the issue
• [x] Labels are assigned to the issue