Make it possible to disable MongoDB fulltext index in 8.10

None of the following actions allows to disable the fulltext with MongoDB:

• setting nuxeo.vcs.fulltext.disabled to false in order to have this line in default-repository-config.xml

  <fulltext disabled="false" searchDisabled="false" />

• removing the line <fulltext disabled="xxx" searchDisabled="xxx" /> from default-repository-config.xml

One of the consequences is that it is not possible not to create the fulltext index for MongoDB
https://github.com/nuxeo/nuxeo/blob/master/nuxeo-core/nuxeo-core-storage-mongodb/src/main/java/org/nuxeo/ecm/core/storage/mongodb/MongoDBRepository.java#L235

It could be interesting not to create the ecm:fulltextJobId_1 index when the fulltext is disabled too => NXP-25203

It should correspond to part of the backport of NXP-24550