feat: adding CourseEnrollmentViewStarted to execute in enrollment view

[kiram15]

Description

This adds a filter CourseEnrollmentViewStarted that will be emitted by the enterprise enrollment view before enrollment is created. We are not reusing the existing CourseEnrollmentStarted filter because this is triggered at the model level, and we want to scoped this to the view-layer enrollment path, not to every programmatic enrollment.

This is part of an ongoing initiative to leverage openedx-filters to allow enterprise to customize logic and remove it from edx-platform code.

Supporting information

Jira ticket - ENT-11570

Testing instructions

Please provide detailed step-by-step instructions for testing this change, including any necessary setup, e.g., additional requirements, plugins, configuration variables, etc, and environment details to ensure the reviewer can test the change.

Deadline

"None" if there's no rush, or provide a specific date or event (and reason) if there is one.

Other information

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• Any other PRs or issues that should be linked here? Any related PRs?
• Any special concerns or limitations? For example: deprecations, security, or anything you think should be noted.

Checklists

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Merge Checklist:

• All reviewers approved
• Reviewer tested the code following the testing instructions
• CI build is green
• Changelog entry added using scriv with short description of the change
• Documentation updated (not only docstrings)
• Code dependencies reviewed
• Fixup commits are squashed away
• Unit tests added/updated
• Noted any: Concerns, dependencies, migration issues, deadlines, tickets

Post Merge:

• Trigger the release workflow to create a new GitHub release.
• Check new version is pushed to PyPI after tag-triggered build is finished.
• Delete working branch (if not needed anymore)
• Upgrade the package in the Open edX platform requirements (if applicable)