Add Maintenance Page Functionality

[neillturner]

Context

Show a friendly message to users when the service is down

Changes proposed in this pull request

• following process Maintenance page
• Configure the maintenance page based on the template for production and a test environment.
• Configure the maintenance page workflow.
• Test the maintenance page in a test environment.

Guidance to review

i retested the workflow
see https://github.com/DFE-Digital/apply-for-qualified-teacher-status/actions/runs/11609667671
and tested the maintenance page came up and app was available on temp url
and
https://github.com/DFE-Digital/apply-for-qualified-teacher-status/actions/runs/11609705432
and tested the maintenance page now gone and app was available again

review changes and test doing the following:

To test workflow - enable

get PIM Access to test

gh auth login

gh workflow run "Set maintenance mode" -r "origin/maintenance-page" -f environment=test -f mode=enable

wait a couple of mins

https://apply-for-qts-temp.test.teacherservices.cloud - should show app

https://apply-for-qts-test-web.test.teacherservices.cloud/ - should show test page

To test workflow - disable

 gh workflow run "Set maintenance mode" -r "origin/maintenance-page" -f environment=test -f mode=disable
``
wait a couple of mins 

https://apply-for-qts-temp.test.teacherservices.cloud - should not exist

https://apply-for-qts-test-web.test.teacherservices.cloud/ - should show show app

#### To test makefile enable

get PIM Access to test

get a github token as per Maintenance page

make test enable-maintenance GITHUB_TOKEN=xxxxxxx

wait a couple of mins

https://apply-for-qts-temp.test.teacherservices.cloud - should show app

https://apply-for-qts-test-web.test.teacherservices.cloud/ - should show test page

To test makefile disable

make test disable-maintenance GITHUB_TOKEN=xxxxxxx

wait a couple of mins

https://apply-for-qts-temp.test.teacherservices.cloud - should not exist

https://apply-for-qts-test-web.test.teacherservices.cloud/ - should show show app

Link to Trello card

AFQTS: maintenance page

Checklist

• Attach to Trello card
• Rebased main
• Cleaned commit history
• Tested by running locally

[Hassanmir92]

Could we have preproduction as an option here too.

Our DR testing will be done on that environment.