Initial version of pgquartz

[sebasmannem]

define a job in a yaml config file

• jobstep can be a shell command or script
• jobstep can be a postgresql query

job can be scheduled cron-like job can be set to only run on:

• master, standby, any
• only one, all parallel, all serialised

option to check a jobs result

• run shell script or command to check
• run sql command to check
• alert when any check fails

[sebasmannem]

Alerting will be taken care of in #31. All other things are taken care of in MVP.