maintenance_mode: stop services

[dacook]

When working on server migrations, I thought that the maintenance_mode.yml playbook should stop/start the relevant services. (Stop when maintenance mode is enabled; start when maintenance mode is disabled)

I think the playbook should stop/start sidekiq. Probably also puma and redis (stopping redis will save dump.rdb for each instance which is helpful for migrations)

This will speed up migrations and remove a step from the server-migration guide:

ofn-install/.github/ISSUE_TEMPLATE/server-migration.md

Line 64 in 0b6be98

- [ ] `sudo systemctl stop sidekiq redis-jobs puma`