Ignore roles for back-dated validation

[niraj2477]

Description

This pull request introduces role-based exceptions for backdated timesheet entry validation and adds supporting configuration for ignored roles within the timesheet module. The main changes include a new Timesheet Role doctype, updates to the timesheet settings to allow configuration of ignored roles, and logic changes to the date validation process.

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Testing Instructions

Additional Information:

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Checklist

• I have carefully reviewed the code before submitting it for review.
• This code is adequately covered by unit tests to validate its functionality.
• I have conducted thorough testing to ensure it functions as intended.
• A member of the QA team has reviewed and tested this PR (To be checked by QA or code reviewer)