Add Column Pinning, Custom View Controls & Fix Costing Rate Calculation

[zeel-codder]

Description

This PR introduces multiple improvements in the Next-PMS app:

• Pinned Columns Support: Enables users to pin columns in tables for improved usability and control over layout.
• Custom View Visibility: Adds support for deleting custom views and toggling their visibility between private and public.
• Employee Costing Rate Update: Refactors the get_employee_costing_rate function in next_pms/project_currency/overrides/timesheet.py by introducing a new parameter for salary calculation and removing currency conversion logic for simplification.

The following changes have also been completed as part of this PR:

• Updated approval message to: "Timesheet approval or rejection has been queued for processing. Please do not make any changes to it. You may continue with other tasks."
• Fields in the Project detail page now support values up to 2 decimal places
• Fixed leave allocation styling in Resource Timeline view for dark mode
• Add fallback icon to viewloader in sidebar

Relevant Technical Choices

• Add Pinned Columns in PMS View Settings doctype to store i.e Array of strings

Updates to employee costing rate calculation:

• Added the date parameter (start_date) to the salary calculation function call, ensuring that the calculation is date-specific.
• Removed the logic for converting the salary currency to the project currency, simplifying the function by eliminating the use of get_exchange_rate.

Testing Instructions

• Go to NPMS
• Try Pinning columns in Project and Task page
• Try Creating views , make private views public or delete them

Additional Information:

Public views cannot be deleted or changed back to private from NPMS.

Screenshot/Screencast

Resource Timeline:

Project Detail

Fallback Icon in ViewLoader

Column.pinning.webm

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)

Addresses: https://github.com/rtCamp/erp-rtcamp/issues/2394