Feature: [Android] have different application IDs for flavors

[rileychh]

Description

• Currently the "beta" flavor and the "real" flavor have the same application IDs (club.ntut.npc.tat)
• This prevents having the debug version and the Play Store version at the same time.
• We should have different suffixes for different flavors.

How to implement?

• Add applicationIdSuffix for each flavor in build.gradle.

Design(optional)

• club.ntut.npc.tat.real for the real flavor
• club.ntut.npc.tat.beta for the beta flavor

Additional contexts(optional)

• I am not sure about if iOS have this issue, since I don't have an iDevice.