Backup failure when using %d on db_filter

[pedrocs-exo]

Since #286, file common.yaml.jinja contains this:

services:
backup:
environment:
DBS_TO_INCLUDE: "{{ odoo_dbfilter }}"

meaning that databases will be backed up only if they match the odoo_dbfilter regular expression. However, on multi-tenant deployments, it's quite common to have a value of ^%d$ on that parameter leading to a configuration where no database backups will be performed.

Replacing it with odoo_dbname doesn't work either. We may want to use values like db1,db2,dbx. and that also disables backups.

IMHO a better solution would be to turn it into a user defined param. And it's default value could eventually be the result of replacing comma (,) by pipe (|) on odoo_dbname. For example: db1,db2,dbx would become db1|db2|dbx. It would work for single databases as well as for database lists.