Document new pum upgrade functions

[ponceta]

It is much easier to dump and restore a production database to a test data base and run the upgrade process on it than to run the entire test-and-upgrade procedure.

New way of doing could be :

pum dump -p pg_qgep /var/tmp

pum restore -p pg_qgep_test /var/tmp

pum upgrade -p pg_qgep_test -t qgep_sys.pum_info -d ./delta/ -v int SRID 2056

See actual procedure :

https://qgep.github.io/docs/en/admin-guide/db-update-pum/index.html#

Let the testing approach for CI and debugging only.

[sjib]

@ponceta Can you update the docs with this or close the issue if not relevant anymore?