* Verify the MySQL driver download to avoid man in the middle attacks

* Fix bug

* Added comment

Merge branch 'TeoGoddet-fix-db-env' of https://github.com/TeoGoddet/docker-xwiki into TeoGoddet-TeoGoddet-fix-db-env

* Commit generated files too

XDOCKER-131: docker-entrypoint doen't set database

* Fix syntax

The documentation was not entirely clear about the need to create directories for bind mounts for the database and application containers, so I've added some context hear for the avoidance of doubt.

I've also added a warning in each case to ensure that fully-qualified directory names are passed.  If you pass a multi-level relative path, you'll get an error message, but if you specify only a single word for a directory, there's an amusing edge case with Docker Desktop, where this gets used as a name, and the mount is managed inside the hidden docker desktop container, which can cause confusing side-effects.

* Use the same collation as xwiki does by default

  * Put new 12.0 version and remove old 10 version not supported
    anymore.

  * Missing update of docker-compose so that the build don't put back
    12.1-alpine

[Misc] Upgrade to latest 12.x version of PostgreSQL to reduce maintenance but also to match the JDBC driver used in the XWiki docker image.