Explain "changeToken" in the context of downloading files

See: https://doc.nuxeo.com/nxdoc/downloading-files/

There is an undocumented param for the file download servlets named "changeToken". This param is used by the client so that an old version is not cached if the document changes.

Note: this param may apply to other endpoints, I'm not sure, but I can't find any doc about it.

Warning: there is also a "changeToken" used on the backend, documented here:

https://doc.nuxeo.com/nxdoc/rest-api-entity-types/#result-of-a-get-request