update: check for new versions in coolwsd not client

[mmeeks]

While it is rather easier to check for updates in the browser when an admin logs in, we should instead fetch the data once inside coolwsd - and then present it to the admin cf. ticket #4489

Thanks.

[mmeeks]

We should also add a setting to turn the update-check off while I think about it =)

[juliusknorr]

This would be awesome, we see outdated collabora versions quite a lot. Having a check on the server could expose a new version through capabilities and we could actually notify admins in the Nextcloud universe that they should upgrade their collabora server.

[szaimen]

Please also make this notification optional as e.g. AIO manages the updates on its own and might be a bit behind...