Implement support to let user define the custom scheduling freqency

[ymaheshwari1]

What is the motivation for adding/enhancing this feature?

In some cases, user may need to define some custom frequency, and for this case we need to have some kind of support to let user easily define the frequency.

What are the acceptance criteria?

• ...

Can you complete this feature request by yourself?

• YES
• NO

Additional information

Use Cron Expression Generator for defining custom frequency. Below is the list of possible options:

https://medium.com/js-dojo/getting-start-with-vue-scheduler-b9a91bd4d14e
https://morioh.com/a/eea3014c18e0/easy-cron-editor-for-vuejs
https://karoletrych.github.io/vue-cron-editor/
https://github.com/abichinger/vue-js-cron

[ymaheshwari1]

For converting cron-expression to human readable expression, we can use this npm package: https://www.npmjs.com/package/cronstrue

https://www.npmjs.com/package/cron-converter

[dt2patel]

Moving to dev complete so that @Adameddy26 can pick for testing