Store freezer logs in Elasticsearch

In order to see what happened in a job (backup, restore, admin) we need to read the logs, and those logs are stored in the filesystem of the machine where the backup was taken.

So, this bp proposes to store those logs in Elasticseach.

In order to do that we need to:

1. Create a new type in elasticsearch similar to /freezer/jobs but for logs /freezer/logs
2. Send the logs from the scheduler to the api
3. Store the logs from the api in elasticsearch

Components affected by this change:
Freezer-agent
Freezer-web-ui
Freezer-api