Achievement: Use moment.js for DateHelper

[jetkan-yk]

Refactor Achievement Date Helper

https://github.com/source-academy/cadet-frontend/blob/c3be01c77969650c10915babcfc2ee77ed26aa16/src/commons/achievement/utils/DateHelper.ts#L1-L64

Use moment.js to prettify dates and deadlines, since it is used by the common Date Helper

https://github.com/source-academy/cadet-frontend/blob/c3be01c77969650c10915babcfc2ee77ed26aa16/src/commons/utils/DateHelper.ts#L1-L43

[jonas-chow]

Working on this