refactor: Do not consider payroll frequency in timesheet based payroll

[saurabh6790]

Issue:

When we set Salary Based On Timesheet attr on Salary Structure or on Payroll Entry, the system hides the field Payroll Frequency.

On Salary Structure the default frequency it Monthly. But as field is hidden there is no way that user will understand this. So at the time of fetching employees on payroll entry, the system were throwing error "Employees not found for selected criteria's"

This issue is due to multiple small issues

1. Bad UX : Field position
2. There is no impact of payroll frequency, when payroll is based on timesheet though the filters are considering payroll frequency

Fix:

1. Set Payroll Frequency to null if its based on timesheet
2. Do not consider frequency in filters
3. Fix field positioning

no-docs

[codecov-commenter]

Codecov Report

Merging #612 (3fb2708) into develop (23871f4) will increase coverage by 0.08%.
The diff coverage is 100.00%.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #612      +/-   ##
===========================================
+ Coverage    72.47%   72.55%   +0.08%     
===========================================
  Files          193      194       +1     
  Lines         9947     9980      +33     
===========================================
+ Hits          7209     7241      +32     
- Misses        2738     2739       +1     

Impacted Files	Coverage Δ
...rms/payroll/doctype/payroll_entry/payroll_entry.py	79.92% <100.00%> (+0.22%)	⬆️
hrms/payroll/doctype/salary_slip/salary_slip.py	87.02% <100.00%> (+0.11%)	⬆️

... and 7 files with indirect coverage changes

[ruchamahabal]

@saurabh6790 added some fixes:

1. payroll frequency condition was also present in the salary slip, which was not changed in this PR. So salary slip creation was failing as it could not find any salary structure. Rectified that condition

2. One more error encountered while running payroll:

   

3. Fixed some typos

4. Replaced payroll frequency validation with mandatory depends on config in doctype schema.