refactor: Leave Control Panel

[krantheman]

Closes: 782

Changes

• Select Employees from a datatable populated with filtered employees as opposed to from a single Link field
• Allocate Leave directly (by specifiying Leave Type), or via Leave Policy Assignment (Integration of Bulk Leave Policy Assignment)
• Selection of dates based on Leave Period, Joining Date, or Custom Range
• Other UI/UX changes

Allocation of leaves via Leave Policy

Allocation of leaves by selecting Leave Type

Docs: https://frappehr.com/docs/v14/en/leave-control-panel

[codecov-commenter]

Codecov Report

Merging #809 (35447a4) into develop (7090b9b) will increase coverage by 0.75%.
Report is 163 commits behind head on develop.
The diff coverage is 83.20%.

@@             Coverage Diff             @@
##           develop     #809      +/-   ##
===========================================
+ Coverage    72.98%   73.73%   +0.75%     
===========================================
  Files          194      195       +1     
  Lines         9990    10349     +359     
===========================================
+ Hits          7291     7631     +340     
- Misses        2699     2718      +19     

Files	Coverage Δ
...leave_policy_assignment/leave_policy_assignment.py	88.02% <100.00%> (ø)
...doctype/leave_control_panel/leave_control_panel.py	82.48% <82.94%> (+82.48%)	⬆️

... and 23 files with indirect coverage changes

[ruchamahabal]

Now the only thing that's stopping us from replacing Bulk Leave Policy Assignment dialog with this panel is the flexible filter group for applying filters on any employee field:

Can you add this? For reference check Dashboard Chart:

Or Data Export:

https://github.com/frappe/frappe/blob/f2277b9254022e2e2365e01bd1ee1bb05288e844/frappe/public/js/frappe/data_import/data_exporter.js#L131-L138

Use frappe.FilterGroup