[IMP] hr_timesheet,sale_timesheet: improved reporting features

Purpose of the commit is to improve the timsheets's report
of the timesheet app.

So in this commit, done the below changes:
- timesheets by billing type report:
 - add default group by date month > billable type.
 - removed undefine value from report
 - improve helper the to: "No data yet! \n Track your timesheets by
    billing type and make sure your time is billable."
 - added grid, kanban and list view
- list view opened through the graph/pivot view: change the name of the action to 'Timesheets'
- improved name of the report to 'Timesheet by employee'
- improved helper of Timesheet by project report
- Timesheet / Attendance report:
 - disabled list opening after clicking graph view.
 - added a group by Employee on report ,
 - modified pivot view according to company of user.
 - added default measure is total difference' and the default group by
   is date > month for report

closes odoo/odoo#75026

Taskid: 253134
Related: odoo/enterprise#20397
Signed-off-by: LTU-Odoo <IT-Ideas@users.noreply.github.com>