docs(plans): record the third batch of phase 6 step MRs in the status table

Step MRs carry no plan-file edits, because the Status rows are adjacent lines of one table and conflict pairwise at merge, so this branch is the single writer for the third batch of rows.

Tracked by Fill the S17 Phase 6 plan Status rows for the o... (#642) • Hayley Swimelar • 19.3

Related to #314