Release 3335

Trello card

https://trello.com/c/E83HBQc9/2189-gse-plan-for-dr-test

Context

Add maintenance page functionality

Changes proposed in this pull request

Add required files from service template

review section will be removed before merge

Guidance to review

• check https://get-school-experience-review-pr-3335.test.teacherservices.cloud looks ok
• make review enable-maintenance PR_NUMBER=3335 GITHUB_TOKEN=xxx
• https://get-school-experience-review-pr-3335.test.teacherservices.cloud should now show the maint page
• confirm temp url shows the web app
• make review disable-maintenance PR_NUMBER=3335 GITHUB_TOKEN=xxx
• https://get-school-experience-review-pr-3335.test.teacherservices.cloud should now work as normal
• temp url should return 404