Setting resource should be optional for JsonItemReaderBuilder

[davemrunal]

As suggested by @benas, creating this issue.

Detailed description on this StackOverflow question

[santfirax]

Hello @davemrunal @benas I would like to work in this issue

[fmbenhassine]

@santfirax Thank you for your suggestion to help! I assigned it to you. Looking forward to your PR.

[santfirax]

@benas I'm having some problems running the unit tests in JsonItemReaderBuilderTest class, could it be possible that you show me how to run this tests?

[santfirax]

Hello @benas @davemrunal here's the PR #3739