Enhance migration rollbacks

To Rollback the database to a previous version, a user must know its internal identifier. There is however no way to discover these ids.

This can be solved by adding:

1. aliasing the latest migration of a version to the name of that version to ease migrations and rollbacks:

   # Instead of 
   waarp-manager db migrate down 20220228
   # do
   waarp-manager db migrate down 0.15.0
   
   # Instead of 
   waarp-manager db migrate up 20220423
   # do
   waarp-manager db migrate up 0.16.0

2. a list subcommand to migrate to list all known migrations. For example:

   $ waarp-manager db migrate list
   0.16.0   20220423   Does foo
            20220301   Does bar
   0.15.0   20220228   Does baz
   [...]