JVM default Locale should be set to parse the datetime

[nusjzx]

parseInstant method in TimeHelper class is using DateTimeFormatter.ofPattern to create format pattern which uses the JVM default locale. For locale like Japan Korea, and China, it cannot parse the date time string correctly

• Environment: master branch at commit Inconsistent labelling of recycle bin #9832

Steps to reproduce

1. You can either change operating system locale, which is JVM default scale, or add Locale.setDefault(Locale.CHINESE); in parseInstant method in src\main\java\teammates\common\util\TimeHelper.java
2. start the app engine
   3.login as administrator and add instructors

Expected behaviour
should add the instructors correctly

Actual behaviour

[nusjzx]

@damithc Although there is a solution in trouble shooting, which was to change the date system default date time format. We can actually handle this configuration in code, instead of let the developer change their default settings individually.

[wkurniawan07]

@nusjzx The dev troubleshooting guide is severely outdated. That aside, configuration inside code is very much preferred over tampering with dev's local machine.