Update file upgrade-to-26.0.8.16 smu.md

# To upgrade from ecloud 25.0.8.19 to 26.0.8.16

- As usual, upgrade your OS with latest patchs, optionally take backup/snapshot

  - NB: you may want to filter out incomming email (TCP 25 & 587) during this upgrade, to avoid losing any messages in case of a rollback

- Go to `/mnt/repo_base`, then run:

  - `docker-compose stop`

  - `git pull origin master`

- In your `docker-compose.yml` file update the following:

  - Set the nextcloud image to `registry.gitlab.e.foundation/e/infra/ecloud/nextcloud/selfhost:26-0-8`

  - Set the mailserver image to `mailserver2/mailserver:1.1.15`

- In your `config/nginx/sites-enabled/nextcloud.conf` change the following:

  - replace all occurences of `oc[ms]-provider` with `ocs-provider` (2 occurences, lines 83 & 98) (reference: https://github.com/nextcloud/server/issues/40803#issuecomment-1751717926)

- Run `docker-compose pull`

- If pulls are OK, run `docker-compose up -d`

- Examine `docker-compose logs --tail=500 nextcloud` for the following messages:

  - `nextcloud       | Upgrading nextcloud from x.x.x.x ...` (x.x.x.x is your previous Nextcloud version)

  - `nextcloud       | Update successful`

- Run:

  - `docker-compose exec -T --user www-data nextcloud php occ db:add-missing-indices`

  - `docker exec -u www-data nextcloud /var/www/html/occ -f app:enable bruteforcesettings`

  - `docker exec -u www-data nextcloud /var/www/html/occ -f app:enable suspicious_login`

  - `docker exec -u www-data nextcloud /var/www/html/occ -f app:enable twofactor_totp`

  - `docker exec -u www-data nextcloud /var/www/html/occ -f app:enable user_backend_sql_raw`

  - `docker exec -u www-data nextcloud /var/www/html/occ config:system:set main_domain`

- Check all settings subsections starting from `/settings/admin/overview` while logged in with the admin user account to identify any issues found post upgrade