Allow customers using Nuxeo Cloud to use WOPI whatever domain they use

Customers using Nuxeo Cloud must be able to use WOPI whatever domain they use: for instance, the integration should work with "myApp.bigcorp.com" and/or "bigcorp.nuxeocloud.com".

We assume that our cloud customers always have a domain name accessible on *.nuxeocloud.com, thus accessible by Office Online.

We need a nuxeo.wopi.baseURL nuxeo.conf property pointing to the nuxeocloud.com domain, such as https://bigcorp.nuxeocloud.com/nuxeo.
Will be used at least for:

• wopiSrc
• the PutRelativeFile URLs