Better messages when the platform starts

[sduenas]

The current messages displayed when the platform starts are the uwsig boot log messages. We need a better way to display that GrimoireLab is running and performing all its booting tasks.
This also applies to others such as workers, consumers, and producers.

[sduenas]

We added structlogs on chaoss/grimoirelab-core#60 . This will allow us to have structured logs.