This change allows the number of sidekiq processes and which job classes
they handle to be configured.
An instance admin may choose to have separate sidekiq processes handling
jobs related to local users (`default` job class) and jobs related to
federation (`push`, `pull`, `ingress`), so that as the instance grows
and takes on more federation traffic, the local users' experience is not
as impacted.
For more details, see https://docs.joinmastodon.org/admin/scaling/#sidekiq
This pr also includes the following changes suggested in review:
- adds syslog identifiers for mastodon services
- moves working directory config to common cfgService
- adds mastodon.target
