PCHR-4110: Fix calendar feeds leave requests inclusion logic

[igorpavlov-zz]

Overview

This PR fixes an issue when some leave requests are not included in a calendar feed due to their "from" and "to" dates.

The table below shows which leave requests were expected to be added but were not added.

              TODAY     +3 MONTHS           NOW    EXP    BUG
    ------------|-----------|------------    
LR1   +++++++                                X      X
LR2          +++++++                         X      V     YES
LR3                +++++++                   V      V
LR4                      +++++++             X      V     YES
LR6                            +++++++       X      X
LR7   ++++++++++++++++++++++++++++++++       X      V     YES

Technical Details

Logically wise the date selection was wrong, the correct logic is:

Whenever at least one day of a leave request appears in the period [TODAY - TODAY+3MONTHS] - include it.

private function getLeaveRequests() {
  $params = [
    // ...
    'from_date' => ['<=' => $this->endDate->format('Y-m-d H:i:s')],
    'to_date' => ['>=' => $this->startDate->format('Y-m-d H:i:s')]
  ];

  $result = civicrm_api3('LeaveRequest', 'get', $params);

  // ...
}

---

✅Manual Tests - passed
⏹Jasmine Tests - not needed
⏹JS distributive files - not needed
⏹CSS distributive files - not needed
⏹Backstop tests - not needed
✅PHP Unit Tests - amended and passed

[ajesamson]

Approved 👌