[Propose] [Need Discussion] Allow user to manually add calculated columns

[GalvinGao]

What problem does this feature solve?

Users may found helpful when having additional calculated columns in which they could specify calculation formula by themselves.

What does the proposed API look like?

Have a calculated column adder which allows user to input the formula (e.g. referencing current stage data, referencing current row data, etc,.) and display the calculated column accordingly.

[GalvinGao]

With the new v4 frontend, such feature shall be more feasible for implementation, but still unknown for user stories to support such feature with evidence. Leaving untouched for now and still open to discussion.