feat: add filter in CourseEnrollmentAllowed.

[anfbermudezme]

Description

This PR adds the enrollment filter into CourseENrollmentAllowed to apply license enforcement when a license reach the purchased seats.

Changes Made

• Add filter in enroll_email function where the enrollment allowed is triggered.

PR related

• https://github.com/Pearson-Advance/course_operations/pull/229

How to test

• Start openedx services with course operation and license enforcement
• Create institution, institution admin and a license with 0 purchased seats
• Add the following setting in lms/envs/common.py

OPEN_EDX_FILTERS_CONFIG = {
    "org.openedx.learning.course.enrollment.started.v1": {
        "fail_silently": False,
        "pipeline": [
            "pearson_course_operation.pipeline.EnforceLicense",
        ]
    },
}

• Create a CCX created from the master course of the license created.
• Try to Enroll a student or Pending student, using the institution portal being Global Admin and Institution Admin. Using the instructor membership tab being Global Admin and being Institution Admin using the ccx_coach tab of the CCX.
• Verify that the enrollment is not executed.
• Add 1 purchased seat into the License, repeat the proccess and then try to add another one. We expect that the purchased seats limit the enrollments.