Add option to load custom ObjectMapper from service

[Michael1993]

Would love some feedback.

Proposed commit message:

Add option to customise ObjectMapper (#704, #740 / #741)

This PR solves the need to be able to customise the ObjectMapper
in JSON based tests, e.g.: load in services. It also adds the option
ALLOW_TRAILING_COMMA.

Closes: #704, #740
PR: #741

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[Bukama]

A general approve, but I suggest to also add tests for the JsonReadFeature.ALLOW_TRAILING_COMMA feature request of #740 which you also added here.

[Michael1993]

A general approve, but I suggest to also add tests for the JsonReadFeature.ALLOW_TRAILING_COMMA feature request of #740 which you also added here.

Good catch. Added.

[Bukama]

A general approve, but I suggest to also add tests for the JsonReadFeature.ALLOW_TRAILING_COMMA feature request of #740 which you also added here.

Good catch. Added.

As I approved, you can merge if you don't have anything else you want to change. I'll be online back tomorrow so feel free to do today.