Schema for recurring tasks

[Yadunund]

Starting a discussion on the schemas for recurring tasks which is needed for open-rmf/rmf_ros2#103

We can have four types of schemas for standard CRUD operations. Common across these will be a sub-schema for describing the periodicity of the tasks and @aarushg22 suggested mimicking the cron datetime format for this.

{
  "seconds" : "0",
  "minutes" : "0",
  "hours" : "15",
  "day_of_week" : "1",
  "month" : "0",
  "day_of_month" : "*",
  "start_date" : "2022-01-01", 
  "end_date" : "2022-01-31"
}