Track application link clicks

[KyleMacPherson]

Trello card URL

Part of https://trello.com/c/vqKrPa54/3137-spike-we-want-a-mechanism-to-count-hard-to-fill-roles-so-we-can-show-them-to-jobseekers

Changes in this PR:

This ticket adds a new field to track the number of jobseekers that click an apply link which takes them to a school or college's own application form.

Screenshots of UI changes:

Before

After

Checklists:

Data & Schema Changes

If this PR modifies data structures or validations, check the following:

• Adds/removes model validations
• Adds/removes database fields
• Modifies Vacancy enumerables (phases, working patterns, job roles, key stages, etc.)

If any of the above options has changed then the author must check/resolve all of the following...

Integration Impact

Does this change affect any of these integrations?

• DfE Analytics platform
• Legacy imports mappings
• DWP Find a Job export mappings
• Publisher ATS API (may require mapping updates or API versioning)

User Experience & Data Integrity

Could this change impact:

• Existing subscription alerts (will legacy subscription search filters break?)
• Legacy vacancy copying (will copied vacancies fail new validations?)
• In-progress drafts for Vacancies or Job Applications

[github-actions]

Review app deployed to https://teaching-vacancies-review-pr-9209.test.teacherservices.cloud on AKS

[scruti]

Nice!