feat: allow mid-period leave policy change

[JK-1117]

Feature Overview: Added the ability to allow mid-period policy changes to enable changing an employee's leave policy assignment in the middle of a period. For detailed use cases, refer to issue Closes #640 .

Implementation Details:

• Added a checkbox labeled "Allow mid-period policy change" in the Leave Policy Assignment.
• When this checkbox is ticked, the following actions occur before submit:
  • Validates if there are any leave applications that span across the old and new Leave Allocations.
  • Updates the end date of the old Leave Policy Assignment, Leave Allocation, and Leave Ledger Entry.

User Impact:

• A new checkbox "Allow mid-period policy change" is added in the Leave Policy Assignment form.

• If the new checkbox is ticked, upon submitting the Leave Policy Assignment, a confirmation dialog will appear to warn the user that this action is irreversible.

Testing: Unit tests have been written to ensure:

• An error is prompted if there are leave applications that span across both Leave Allocations.
• After changing the Leave Policy, the new leave balance is accurately reflected.

[JK-1117]

Hi @ruchamahabal , I would like to contribute to the Frappe HR documentation. When I tried to edit it, I was prompted to log in, but I couldn't find a registration page. Could you guide me on how to create an account? Also if you have any suggestions or concerns regarding the changes I proposed, please let me know.