@sourceloop/core: CreatedOn and ModifiedOn columns should not be data driven

[yeshamavani]

Describe the bug
CreatedOn and ModifiedOn columns should not be data driven
These values should always be a the current date and user should never be able to change its value based on input.

To Reproduce
Steps to reproduce the behavior:

1. Hit any post API where the base model entity is UserModifiableEntity
2. Pass the createdOn and modifiedOn date values as some backdated data
3. Observe the entry in database
4. Instead of current date the values will be one provided in input

Expected behavior
Should always be the current date time.