OnlyOffice and Seafile apps compete over port 8000

[devillemereuil]

When installed together on the same server (although with different subdomains), Seafile and the OnlyOffice DocService compete for the same port. They both use port 8000 by default:
https://manual.seafile.com/deploy/using_firewall/
https://helpcenter.onlyoffice.com/fr/installation/docs-community-open-ports.aspx

This means that, when they are co-installed on the same server, one of them is blocking the other (Seafile seems to start first o my server and blocks OnlyOffice). This results in a "BAD REQUEST 400" when using the healthcheck of OnlyOffice
https://onlyoffice.jenepi.net/healthcheck/

If Seafile/Seahub are stopped, then it is possible to connect to the Document Server, including from Nextcloud (yes, for some reason, I use both Seafile and Nextcloud).

A possible solution to this conflict is to allow for choosing the port the OnlyOffice DocService is using, which would be different from port 8000.

[devillemereuil]

I'm linking the similar bug report for Seafile:
YunoHost-Apps/seafile_ynh#111

[devillemereuil]

For future reference, I seem to have this issue fixed by changing port 8000 to another port for step 2 and 3 of the following guide:
https://afterlogic.com/docs/aurora/frequently-asked-questions/configuring-onlyoffice-docs-with-non-standard-port

More precisely, changing the port 8000 to something else in "services" > "CoAuthoring" > "server" configuration in /etc/onlyoffice/documentserver/default.json and changing also the port in /etc/onlyoffice/documentserver/nginx/ds.conf seems to have fixed the issue after rebooting. I'm afraid it would not stick after an update however?