Define alias for configured adapters

Would be nice, if I can tell this bundle to also register one adapter under several other names. For some reason we have setup several different adapters for several components, but at the end everyone still uses the same memcache. Instead of repeating the settings over and over again I thought of something like

    liip_doctrine_cache:
      namespaces:
        # name of the service (aka liip_doctrine_cache.ns.foo)
        foo:
          # cache namespace is "ding", this is optional
          namespace: ding
          # cache type is "apc"
          type: apc
          alias: [bar, baz]

Now we should have `liip_doctrine_cache.ns.foo`, liip_doctrine_cache.ns.bar` and `liip_doctrine_cache.ns.baz`, that all actually refer the same adapter. Maybe it should be possible to define "fully qualified service IDs" too, but that isn't as important, as well as the format of the config. :smile: