Feature: Difference between 2 dates in days

[koratalas]

This is a new feature that is introduced to find the difference between two dates provided by the user. This is most commonly used by the developers while sending out the notifications to show that the ticket is open since "x" no. of days, etc.

So, the functionality of this feature is pretty simple, straight forward and is as follows:

1. user provides the start and end dates to the action.
2. action takes dates converts them to numeric values and then checks if the end date is greater than start date or not, if end date is less than start date then it throws error: "End date is less than start date, please validate.".
3. if end date is greater than start date then it will calculate the difference and sends it to the output.

Example scenarios:

1. Leave requests to show the managers, how many days is the leave being applied for.
2. User onboarding notifications, etc.

[github-actions]

✅ Valid PR for ActionPack

Thank you for your contribution. This PR complies with the CONTRIBUTING.md.
A maintainer will review this shortly. In the meantime, Happy Hacking!

[am-shakeel]

Looks good