Issue:
[BUG] Remove default values for created_at and modified_at from the database

# Context
Currently we are setting `created_at` and `modified_at` in the database during insert through Posgresql `now()` function which gives the current time according to the current time zone. But when we modify the data we pass `common_utils::date_time::now` to update modified at which gives the date time in UTC.

# Resolution
Remove default values for `created_at` and `modified_at` from database and add it in `DatabaseStructNew` struct. Which forces the developer to pass these values while inserting, which fixes inconsistencies of these two values between database and application

Resolution:
<think>
PR Context:
- Title: fix: remove defaults from `created_at` and `modified_at`
- Merged: 2023-05-02T20:45:30Z
- Files changed: 12 files
- Commits: 1 commits

Implementation approach:
## Type of Change
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- [x] Bugfix

## Description
<!-- Describe your changes in detail -->
This closes #984 

### Additional Changes
- [x] This PR modifies the database schema

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## Motivation and Context
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</think>

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