Mattermost - Add affinity docs

Sub issue for https://repo1.dso.mil/platform-one/big-bang/bigbang/-/issues/284

added Affinity/AntiAffinity mattermost priority4 labels

created merge request !16 (merged) to address this issue

mentioned in merge request !16 (merged)

changed iteration to Big Bang Iterations Mar 30, 2021 - Apr 5, 2021

added statusdoing label

changed milestone to %1.5.0

set weight to 1

added statusreview label and removed statusdoing label

mentioned in commit 159df461

closed with merge request !16 (merged)

reopened

added statusdoing label and removed statusreview label

Reopening to modify the values spec.

mentioned in merge request !19 (merged)

added statusreview label and removed statusdoing label

mentioned in commit 271923eb

closed with merge request !19 (merged)

removed statusreview label