Add a warning about MongoDB 4.4 in the compatibility matrix

The page https://doc.nuxeo.com/nxdoc/compatibility-matrix/ indicates that Nuxeo 10.10 supports MongoDB from 3.4 to 4.2, thanks to the upgrade of the MongoDB driver to 3.12.1

However we won't be able to upgrade more, as MongoDB Driver 4.1 brings breaking changes.

So we must add a warning related to the sentence "Nuxeo Platform will likely work with greater versions of the aforementioned databases" to indicate that MongoDB 4.4 and later will never be supported by Nuxeo 10.10