Change "Stop" to "Pause" in Harbormaster build UI
Summary: Resolves T5814. Ref T1049. This changes "Stop" to "Pause" in the UI (internally it's still referred to as Stop).
Test Plan: Viewed builds and saw the intended wording.
Reviewers: #blessed_reviewers, epriestley
Reviewed By: #blessed_reviewers, epriestley
Subscribers: epriestley, Korvin
Maniphest Tasks: T1049, T5814
Differential Revision: https://secure.phabricator.com/D10172