Add new preparation functions startswith() and endswith()

[mh0203]

Is your feature request related to a problem? Please describe.
There's some needs that to select rows that begin or end with a specific word.

Describe the solution you'd like
Add new preparation rules.

1. startswith(column, 'text'): return True if the column starts with 'text'. else return false.
2. endswith(column, 'text'): return True if the column ends with 'text'. else return false.

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
Add any other context or screenshots about the feature request here.

[mh0203]

See below for how to use the function.

https://tde.sktelecom.com/wiki/display/METATRON/Data+Preparation+Function+List

[mh0203]

이번에 추가된 룰은 startswith와 endswith 입니다. 추가적으로 3.0.5에 추가된 contains에 대한 UI 작업까지 3건 부탁드립니다.

This branch adds startswith and endswith function. Additionally, contains function that added at 3.0.5 also needs UI development.