[609] enabling task: add route for accessing recruitment cycle timetables as html or json

[elceebee]

Context

This is an enabling task for using the RecruitmentCycleTimetable model in the cycle switcher. In order to 'switch back to production dates', we need to be able to get the production dates. The easiest way to do that is to expose them as json in a public page.

There is also an html rendering for reference

Changes proposed in this pull request

Endpoint for rendering all or one recruitment cycle timetable

Guidance to review

Check the following end points in the review app:
publications/recruitment-cycle-timetables?format=json
publications/recruitment-cycle-timetables/current?format=json
publications/recruitment-cycle-timetables/an-invalid-year-like-2018?format=json
publications/recruitment-cycle-timetables/2023?format=json

And then all again, but without the format=json param to see the html response

Things to check

• If the code removes any existing feature flags, a data migration has also been added to delete the entry from the database
• This code does not rely on migrations in the same Pull Request
• If this code includes a migration adding or changing columns, it also backfills existing records for consistency
• If this code adds a column to the DB, decide whether it needs to be in analytics yml file or analytics blocklist, if included inform data insights team of the changes
• If this code adds a column that may include PII, the sanitise.sql script and 0025-protecting-personal-data-in-production-dump.md ADR have been updated
• API release notes have been updated if necessary
• If it adds a significant user-facing change, is it documented in the CHANGELOG?
• Attach the PR to the Trello card

[elceebee]

Using new recruitment cycle timetable for cycle switching

[CatalinVoineag]

Dev tested the endpoints on review, with json and HTML format

[dcyoung-dev]

Nice work! These endpoints will be great for the Reference Data maintainers to auto-generate the cycle timetables 👌