Enables parsing of application/hal+json as JSON

[janhartmann]

This pull requests enables JSON parsing of content type application/hal+json.

https://en.wikipedia.org/wiki/Hypertext_Application_Language

TODO:

• Update CHANGELOG.md with your change (include reference to issue & this PR)
• Make sure all of the significant new logic is covered by tests
• Rebase your changes on master so that they can be merged easily
• Make sure all tests and linter rules pass

[apollo-cla]

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[martijnwalraven]

Thanks, this looks good! I'm happy you also added a new test.

[jonbjk]

I think the solution proposed in #1645
is more general, since it would allow parsing of any JSON response, by making the contentType configurable. In that way we can support for example "application/vnd.api+json" as well as "application/hal+json".

[janhartmann]

I agree, we also need to support different casing, e.g by lower casing.

As og today, if the content type sent back is “Application/Json” it will not parse either. Might need another issue

[jonbjk]

In #1645 I added a field jsonContentType that defaults to "application/json", but that the developer can override (a bit like the baseUrl). I think that that is a simple and flexible solution.
If you look at for example: https://swagger.io/docs/specification/media-types/
a content type such as "application/vnd.mycompany.myapp.v2+json"
is also valid.