Extension compiler pass

Move all related stuff to DIC configuration into compilers ; basically, here what was done :

- Ensured that a `broker` (or `channel_factory` ? There are some naming issue I guess) can be declared as one if it has a `swarrot.broker` tag. This name can be modified though (`swarrot.channel_factory` ?)
- Ensured that a `channel_factory` implements the `FactoryInterface`
- Ensured that the PECL factory is not the only one used when building commands

That is more or less a POC, even though I added some tests.

(Related to #1)