Developer documentation : Add quick guides for running Janssen usecases

[ossdhaval]

After installing Janssen, developers who want to contribute to Janssen will want to setup working usecases end-to-end to see things in action. We need to write guides or small tools, like oxd Spring app, that can help them see end-to-end flow. This can also help developers test their fixes before submitting PR.

Benefit: This will help prospective users quickly understand how easy it is to deploy and configure Janssen for scenarios that are relevant to them. Also, this will help reduce learning curve for new contributors.

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Due: 31st July 2021