Convert interval parameter to cron schedule for self serve replication

[chenselena]

Summary

This PR adds cron schedule to the replication config for the self serve replication API and converts the interval parameter to a cron schedule. Cron schedule is needed as an input for the replication job that performs the cross cluster data copy. The library cronutils is added to perform the cron expression generation.

The interval parameter can be validated as 12H, 1D, 2D, 3D and the cron schedule is generated based on:

• 12H schedule dictates replication should trigger every 12 hours
• The cron schedule should have an X hour to start from midnight where X can range from 0-23 and Y minute where Y is in [0, 15, 30, 45]. E.g 12hours can lead to schedule “0 30 3/12 ? * * *” -> trigger at 3:30am and 3:30pm every day.
• If interval is not provided, a daily replication schedule should be set up with daily schedules with X hour starting from midnight.
• X is randomized from 0-23 and Y is randomized as a value of [0, 15, 30, 45] to spread out the cron and avoid job clusters around a time.

Examples of:
12H: 0 15 23/12 ? * * *
1D: 0 45 10 ? * * *
2D: 0 30 8 ? * */2 *
3D: 0 0 8 ? * */3 *

Changes

• Client-facing API Changes
• Internal API Changes
• Bug Fixes
• New Features
• Performance Improvements
• Code Style
• Refactoring
• Documentation
• Tests

For all the boxes checked, please include additional details of the changes made in this pull request.

Testing Done

• Manually Tested on local docker setup. Please include commands ran, and their output.
• Added new tests for the changes made.
• Updated existing tests to reflect the changes made.
• No tests added or updated. Please explain why. If unsure, please feel free to ask for help.
• Some other form of testing like staging or soak time in production. Please explain.

For all the boxes checked, include a detailed description of the testing done for the changes made in this pull request.

Unit tests added to check that the cron schedule was created successfully.

POST http://localhost:8000/v1/databases/u_tableowner/tables for a 1D schedule:

{
    "policies": {
        "sharingEnabled": "true",
        "replication": {
            "config": [
                {
                    "destination": "clusterA"                
                 }
            ]
        }
    }
}

response:

        "replication": {
            "config": [
                {
                    "destination": "clusterA",
                    "interval": "1D",
                    "cronSchedule": "0 0 10 ? * * *"
                }
            ]
        }

12H schedule:

"replication": {
            "config": [
                {
                    "destination": "clusterA",
                    "interval": "12H",
                    "cronSchedule": "0 0 23/12 ? * * *"
                }
            ]
        }

Additional Information

• Breaking Changes
• Deprecations
• Large PR broken into smaller PRs, and PR plan linked in the description.

For all the boxes checked, include additional details of the changes made in this pull request.

[rohitkum2506]

LGTM, thanks Selena.

[abhisheknath2011]

Thanks @chenselena for addressing the comments!