This commit adds a "Add Custom Field" button on optional columns dropdown list

The goal is to let the user now he can add custom fields to a listview with Odoo Studio,
and to promote Odoo Studio when not installed.

Task: 2392303

**Description of the issue/feature this PR addresses:**
The purpose of this task is to:
let the user know that he can add custom fields to a listview with studio
promote studio when it is not installed

**Current behavior before PR:**
None

**Desired behavior after PR is merged:**

Add a new 'add custom field' button at the bottom of the listview optional fields dropdown (i.e. o_optional_columns_dropdown)
mockup https://drive.google.com/file/d/1o7xGAmxKuE77dqkdteh10v5EAIbHquzj/view?usp=sharing
prefix the button with a fa-plus icon
 - if there is no optional field in the view, display the dropdown with the 'add custom field' button only

This new button is only visible to res.users in base.group_system

When clicking on the 'add custom field' button
  - if studio is installed, open studio on the current view
  - if studio is not installed, the 'add custom field' item unfolds on the studio
    - mockup https://drive.google.com/file/d/1c4cpMmZWlW-IrbXmcH1EaSe0aUnmdHOU/view?usp=sharing
       - it 'unfolds' in the same way the 'add custom group' item of the searchview filter unfolds  
    - video https://drive.google.com/file/d/1VxRZWrX9aeqjVI1XvqnZAxSaULd1-Rt1/view
    - the 'install odoo studio' button directly installs studio
      - it does not redirect to the ir.module.module formview of the studio app
      - you can should reuse the action, image, and link of the existing 'studio' banner https://drive.google.com/file/d/1HWtPiGM8C1LE-nYs9Gt2PObxVr86h9Fr/view?usp=sharing

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A new calendar view has been added, the "year" view.
Some modifications should be done on this view, more specially in "Time Off" application.
Problems were the fact that it was hard to see if a time off has been approved or not or week-ends & public holidays that are not grey.

Another goal with Year view is to display it in a single page without scroll bar.
Before this commit, a scrollbar was displayed on the right of the screen.
This results in some data wasn't displayed on the screen.
Now, the year view is scalled to the browser.
That means that all informations are now on the screen (without scrollbar).

This commit changes year calendar in Time Off module.
More specially, this commit:
- Changes default calendar in personal dashboard to "year"
- Gray week-ends & public holiday (based on the worker's calendar)
- Hatches non-approved time off
- Removed a calendar view from My Time Off Requests
- Fix a "cancel" button that doesn't work
- Add a new view that is displayed when there is no filter to show on the filter view for calendars

"is_hatched" is used to hatch date under specific conditions
The goal was that it was not possible to display some information differently depending on a variable.
Now, if a variable named "is_hatched" is set to true and passed to the calendar view, the specific date is hatched.

This PR also fixes a bug in calendar view: If a filter has a space in his title, we were not able to collapse it.

Task id #[2318645](https://www.odoo.com/web#action=333&active_id=1251&cids=1&id=2318645&menu_id=4720&model=project.task&view_type=form)
Task id #[2317525](https://www.odoo.com/web#action=333&active_id=1251&cids=1&id=2317525&menu_id=4720&model=project.task&view_type=form)


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When a employee begins his first job, this worker can have some european leaves after having worked 3 months in a company. This european leaves is in fact a advance on the double holiday pay in the next year.
This PR adds this deduction in the double holiday pay.
To do this, we check that the employee has taken some european leaves in previous year to reduce the amount of the double holiday. However, if the amount of the double holiday pay is not sufficient, the deduction is made in the following double holiday pay. Thus, we need to check if there are some european leaves 2 years ago (if there aren't a deduction in double holiday pay last year)

**Content of the PR:**

- Set *dmfa_code* for the european leaves to 14 for the DMFA.
- Add belgian company in the european leave type to correctly test the feature.
- Improve the basic salary in the double holiday pay. Because, if an employee just begins at the mid of the previous year, we need to compute the correct paid amount for the double holiday paid. That is, in this case the half of his monthly salary.
- Add sum_worked_days method, to search and sum the amount of the the european leaves in hr.payslip.worked.days in 2 previous years (or last year if there is a deduction in double holiday pay in last year).
- Add rule for the european leaves deduction in *hr_payroll_structure_cp200_double_holiday*.
- fix a negative total for NetOwedAmount tag in DMFA
- Declare the double holiday pay with european leaves deduction (if there is a deduction) in DMFA (Unfortunately, not sure for the structure, so it can be changed in another task).

TaskId: 2337215